Sayyiduna Nu'man bin Bashir (may Allah be pleased with them both) says: My father brought me to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah, bear witness that I have given Nu'man such-and-such from my wealth. He (peace and blessings be upon him) said: "Have you given all your sons the same as you have given Nu'man?" He said: No. He (peace and blessings be upon him) said: "Make someone other than me a witness. Would it not please you that they all be equal towards you in kindness?" He said: Of course. He (peace and blessings be upon him) said: "Then, no."
In the wording of al-Sha'bi (may Allah have mercy on him): "Would it not please you that they be equal towards you in kindness and gentleness?" He said: Yes. He (peace and blessings be upon him) said: "Then make someone other than me a witness to this."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 12001