Once an Arab came in the presence of Holy Prophet (s.a.w.a). He was tensed and upset.
He said, “It’s been two years since I am bestowed with a son. I and my wife are fair complexioned. Yet our son is dark skinned. In these two years I never doubted about my son. But recently someone has instilled this thought in my heart and said, ‘Maybe your wife was unfaithful to you, and this child is not your son, since he does not have the same complexion as you.’ Since that day this thought has engulfed me and made my life miserable. What if my wife has cheated on me and this child is not mine? What should I do?”
The Holy Prophet (saws) said, ”Go out of the city to so and so place. There you will find a young man busy in building a house. Leave your child near him and observe from far. If your son goes close to that man, your son is legitimate. Else he is illegitimate”
The man did as he was told. He went to the city outskirts and found the young Arab as per Holy Prophet’s description. He left his son near that man and stepped away to observe from a distance. The child, who was 2 years old, observed the Arab who was busy in his work. He looked at the things lying around at that place. All the while the father was observing from a distance. His heart was racing and he was anxious to see what his child would do. He saw that his son held the edge of the man’s cloak and pulled it. He spread his hands, so that the man could lift him.
The father saw that the man stopped working. He picked up the child with love and affection. He saw that his son too smiled back and there was a bond that was established between them. His heart was filled with joy and happiness and he felt a sense of great relief.
He could no longer restrain himself. He came out from his hiding place and went near that man. He conveyed his salam to that young Arab and wanted to take the child from his hands. But the child refused to let go and come in his father’s arms.
In the end, the man took his son, asked forgiveness from the man (for having disturbed him in his work), thanked him and bid him goodbye.
He returned to Madina and met the Holy Prophet (sawa) and narrated the entire episode.
Holy Prophet (sawa) said, “Do not doubt your wife. Rest assure that he is your son. It is possible that one of your ancestors was dark skinned. Thus, your son is like him in his complexion.”
The man said, “Yes I am relieved and my heart is at peace. But could you please tell me about that young man who was was busy in building the house?”
The Holy Prophet (sawa), “He is my brother and son of my uncle. He is Ali ibne Abi Talib (as). The one who claims He that he is legitimately born, yet bears enmity towards Ali is a liar.”
Amali Saduq, pg. 209,
Behar Al Anwar, vol. 27, pg. 147.