Al-Sha'bi (may Allah have mercy on him) says that he heard the long story from Nu'man bin Bashir (may Allah be pleased with him), and at its end he said that the Prophet (peace and blessings be upon him) said: "I will not bear witness to this; this is injustice. Make someone else a witness to this. Be just between your children in gifts, just as you love that they be just towards you in kindness."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 12003