وَعَنِ ابْنِ عُمَرَ قَالَ: نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَن بيع الْوَلَاء وَعَن هِبته

Ibn ‘Umar said that God’s Messenger forbade selling or giving away the right to inheritance from a manumitted slave. (Bukhari and Muslim.)