Some of famous sayings of the Holy Prophet of Islam(S.A.W.) regarding the uniqueness and magnificence of Imam Ali(A.S.) as recorded in all the authentic Sunni and Shi'ite sources.
"Whomsoever I have authority over,Ali(A.S.) has also authority over him,
O Allah! befriend whoever befriend him and be hostile to whosoever is hostile to him".
"I am the city of knowledge and Ali(A.S.) is the gate."
"Ali(A.S.) is with truth and truth is with Ali(A.S.).They will never separate until they join at the Pool of Kawthar in the Hereafter"
"Every prophet has a vicegerent and inheritor and Ali(A.S.) is my vicegerent and inheritor."
"You[Ali(A.S.)] are to me as Aaron unto Moses,only there is no prophet after me."
"Only the faithful believer will love you and only hypocrites will hate you."

Birth of Ali(A.S.) in the Holy Kaaba
Hazrat Ali(A.S,) was born in the Holy Kaaba at Mecca on Friday, the 13th day of Rajab, 600 A.D. Both the Holy Prophet (S.A.W.) and Hazrat Ali(A.S.) belonged to the same clan. They were Hashimites, the clan of Bani Hashim. Muhammad's(S.A.W.) father was Abdullah, and that of Hazrat Ali(A.S.), Abu Talib. They were brothers and their father was Abdul Muttalib. Thus the Holy Prophet(S.A.W.) and Hazrat Ali(A.S.) were cousins. Hazrat Ali(A.S.) had two brothers, Ja'far and Aquil.

Hazrat All's mother Fatima was the daughter of Asad,a famous magnate of the Quraish clan. She was also the aunt of the Holy Prophet, being the wife of Abu Talib, the Prophet's paternal uncle. When she was pregnant, she promised Muhammad(S.A.W.) to make over to him whatever child was born to her, be it male or female. Muhammad(S.A.W.), brought forth, gladly accepted the offer.
Ali's holy personality began its wonderful manifestation even during the period of his mother's pregnancy. At that time, Muhanunad(S.A.W.) had not yet announced his prophethood, and yet when he passed before Fatima, who being his aunt was senior to him, she used to stand up in reverence and respect for him, and somehow something within her never allowed her to turn her face away from Muhammad(S.A.W.) as long as he was around.
When people asked her about this peculiar behaviour of hers, she would say that she could not help it, that some irresistible urge from within made her do so.
This statement was disbelieved by those who wished to test her. So one day they made her sit and they asked two strong men to hold her down when Muhammad(S.A.W.) passed by. Then they asked Muhammad(S.A.W.) if he would walk in front of her, to which he gladly agreed. As he came in front of her, Fatima began to rise and she stood erect throwing both men aside. Muhammad(S.A.W.) who alone was aware of this mystery, used to smile.

Holy Prophet(S.A.W.) was keenly awaiting the birth of his cousin Ali(A.S.).
During her pregnancy whenever Fatima was alone, she heard from within her a mysterious whisper which was to the glorification of God.
To understand the significance and importance of his place of birth, it is essential to know a little of the history of the Kaaba.
The first House of God was rebuilt and renovated at the command of Allah by the Prophet Abraham assisted by his worthy successor, his son Ismail, under the supervision and guidance of the Angel Gabriel. The verses of the Holy Qur'an say :
"And remember when Abraham raised the foundation of the House with Ismail, (Praying) Our Lord! accept (this service) from us; verily Thou and Thou (alone) art the All-hearing and All-knowing.
Chap. 2-Verse 127.
"And remember when we made the House a resort for mankind and a sanctuary (saying), Take ye the station of Abraham a place of prayer (For you); and covenanted with Abraham and Ismail (saying) purify ye two my House for those who make the circuit, and for those who prostrate (adoring) .
Chap. 2-Verse 125.
This verse clearly depicts the purpose of the Kaaba, namely that it was to be a place of worship and that it was pure and sacred.
Another indication of Ali's special merit was his birthplace. No one else, from Adam down through all the prophets, possessed such a distinction. Of all human beings, he alone was born in the sacred precinct of the Ka'ba. At the time of the birth of the Prophet Jesus his illustrious mother was forced to leave the Holy House. A voice said to her: "O Mary! Leave the Baitu'l-Muqaddas, since it is the place of worship and not of childbirth."
But when the time of Ali's birth approached, his mother, Fatima Bint Asad, was asked to enter the Ka'ba. She was expressly called to enter the Ka'ba, the door of which was locked.
She went to the Masjidu'l-Haram, where she felt labor pains. She prayed to Allah in the precinct of the Ka'ba, saying: "O Allah! I pray to you in the name of your honor and awe, to put me at my ease in this labor." Suddenly, the wall of the Ka'ba, which was locked, opened.
Another report says that a voice was heard saying: "O Fatima! Enter the House." Fatima went into the House of Allah in front of a crowd of people who were sitting round that place and the wall returned to its original condition. The people were greatly astonished. Abbas was also there. When he saw what had happened, he immediately told Abu Talib because he had the key to the door. He instantly came there and tried his best to unlock the door, but the door did not open.
For three days Fatima Bint Asad remained inside the Ka'ba, apparently without sustenance of any kind. This unusual event was the talk of the town. At last, on the third day, the passage through which she had entered again opened, and Fatima came out. The people saw that she had in her hands a lovely child. Both sects (Shias and Sunnis) agree that no one else had ever been given such distinction.
Hakim in his Mustadrak and Nuru'd-din Bin Sabbagh Maliki in his Fusulu'l- Muhimma, Fasl I, p.14, say: "No one before Ali(A.S.) was born in the Ka'ba. This was a distinction given to Ali(A.S.) in order to enhance his honor, rank, and dignity."

Ali(A.S.) was born a Muslim
On the third day of this happening, with awe the wonder- struck crowds surrounding the Kaaba witnessed the lock falling of its own accord, and to their surprise Fatima emerged radiant from the sacred premises, cheerfully holding her new-born babe in her arms. Muhammad(S.A.W.) was waiting to receive her and her new-born and the first face that little Ali(A.S.) saw in this world was the smiling face of the Apostle of Allah, Muhammad(S.A.W.), whom he greeted thus:
"Assalaamo alaika ya Rasoolallah (Peace be upon thee 0 Prophet of Allah).
Thus it is an undisputed fact that Ali(A.S.) was born a Muslim, and his first words testified to the Prophethood of Muhammad(S.A.W.). Muhammad(S.A.W.) lovingly took him into his arms. Ali's first bath after his birth was given by Muhammad(S.A.W.) with a prediction that this babe would give him his last bath. This Prophecy was fulfilled on the demise of the Holy ProphetS.A.W.). The child accepted no other food other than the moisture of Muhammad's tongue, which he sucked for several days after his birth. Muhammad(S.A.W.) fondled him in his lap in his infancy, and chewed his food and fed Ali(A.S.) on it; he often made him sleep by his side, and Ali(A.S.) enjoyed the warmth of Muhammad's(S.A.W.) body and inhaled the holy fragrance of his breath.
Ali(A.S.) was born in the sanctuary of Allah, to which the devil had no access, he did not cry at birth but was found smiling. Thus God had interposed a veil between the evil spirits and the child who was to grow up to exalt His Holy Name. All has been described as having been found like a priceless pearl in the shell of the Kaaba, or a sword in the sheath of Allah's House, or as a lamp found in Allah's abode shedding light all around.
The sanctified birth of Ali(A.S.), as that of Holy Prophet Muhammad(S.A.W.), was foretold in the scriptures, when God said to Abraham, who asked for a blessing on Ishmael; "And as for Ishmael, I have heard thee: behold I have blessed him, and will make him fruitful, and will multiply him exceedingly, twelve princes shall he beget, and I will make him a great nation. (Genesis 17 : 20).
The felicitous Prophecy in Genesis 17:20 about the advent of a prophet is said to point to the appearance of Muhammad(S.A.W.) and Ali(A.S.). While the Twelve Princes' of the Mosaic Scriptures are held to be none other than the twelve Holy Imams(A.S.).
Hazrat Ali's birth inside the Kaaba is unique. This is the only known occasion on which a child was born within the precincts of the holy place ever since its foundation thousands of years ago.
When Ali(A.S.) was about five years of age, Muhammad(S.A.W.) took him away from his uncle Abu Talib to bring him up as his own child. Thus from his earliest days, Ali(A.S.) came directly under the tutelage of the Apostle of Allah, to share his high ethics and morals. Ali(A.S.) was ever ready to run the risk of his own life for Muhammad(S.A.W.) at times of danger and he was affectionately attached to him with unswerving faithfulness. The cousins were so fond of each other that they lived together till death parted them.
As Hazrat Ali(A.S.) says: "The Holy Prophet brought me up in his own arms and fed me with his own morsel. I followed him wherever he went, like a baby camel which follows its mother. Each day an aspect of his character would beam out of his noble soul and I would accept it and follow it as a command.
Ten years in the company of Muhammad(S.A.W.) had kept him so close and inseparable that he was one with him in character, knowledge, self-sacrifice, forbearance, bravery, kindness, generosity, oratory and eloquence. From his very infancy, he prostrated himself before God along with the Holy Prophet, as he himself said,
"I was the first to pray to God along with the Holy Prophet.
According to Ibne-e-.Maja page 12, Raiz-un-Nazarah Vol. II page 158, Usdul Ghaba Vol. IV page 1, and Izalathul Khafa un Khilafatul Khulafa page 252, Ali(A.S.) used to say :
"I have prayed to Allah along with the Holy Prophet(S.A.W.) seven years before any other person did.
The First Believers : Ibn Abbas, Anas. Zaid bin Aqram, Salman Farsi, and others have said, "Indeed it was Ali(A.S.) who was the first to declare his Islam, and some say that there is a consensus for this!Major Jarret's translation of Suyuti's History of the Caliphs page 171.
The Illustrious Ali(A.S.) was thus the first to readily embrace Islam and testified to Muhammad(S.A.W.) being the Apostle of Allah.
Often did the Holy Prophet(S.A.W.) go into the depths of the solitary desert around Mecca with his wife Khadija and his young cousin and disciple, Ali(A.S.), so that they might together offer their thanks to their Allah for His manifold blessings.