I was informed that he (the Holy Prophet) cursed the one who did that (and it was recorded) in his Sahifa (in a document).
Sahih Muslim Book 20, Hadith 21
← Previous Hadith This hadith has been narrated on the authority of Ibn 'Umar (Allah be pleased with them) through another chain of transmitters but with this change that in tba hadith narrated by al-Thaqafi from Ubaidullah there is only a mention of selling (or right of inheritance, al-Wala' ) but not that of making a gift.

Sahih Muslim Book 20, Hadith 20 Next Hadith → He who takes anyone as his ally without the consent of his previous master, there will be the curse of Allah and that of His angels upon him, and neither, any obligatory act of his nor the supererogatory one will be accepted (by Allah).

Sahih Muslim Book 20, Hadith 22