My father took me to the Messenger of Allah (ﷺ) and said to him: "I have gifted one of my slaves to this son of mine." The Messenger of Allah (ﷺ) said, "Have you given such gift to every son of yours?" He replied, "No." Thereupon he said, "Take this gift back."

Another narration is: The Messenger of Allah (ﷺ) said, "Be mindful of your obligation to Allah and do justice in respect of your children." My father came back and revoked his gift.

Another narration is: The Messenger of Allah (ﷺ) asked, "Have you other children besides this one?" He said, "Yes." The Messenger of Allah (ﷺ) asked, "Have you awarded a gift like this to all of them." He said, "No." The Messenger of Allah (ﷺ) said, "I am not going to bear witness to this act of injustice."

Another narration is: The Messenger of Allah (ﷺ) asked, "Do you not except goodness from all of them as you except from him?" He said, "Yes, of course." The Messenger of Allah (ﷺ) said, "Then don't do this (i.e., do not give a gift to one son only)."

[Al-Bukhari and Muslim].