Sahih Muslim , Book 20, Hadith 21 (In-Book) ⓘ

Jabir b. Abdullah (Allah be pleased with them) reported that Allah's Apostle made it obligatory for every tribe (the payment) of blood-wit; he then also made it explicit that it is not permissible for a Muslim to make himself the ally (of the slave emancipated by another) Muslim without his permission. He (the narrator further added): I was informed that he (the Holy Prophet) cursed the one who did that (and it was recorded) in his Sahifa (in a document).

وَحَدَّثَنِي مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، أَخْبَرَنِي أَبُو الزُّبَيْرِ، أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ، يَقُولُ كَتَبَ النَّبِيُّ صلى الله عليه وسلم عَلَى كُلِّ بَطْنٍ عُقُولَهُ ثُمَّ كَتَبَ ‏ "‏ أَنَّهُ لاَ يَحِلُّ لِمُسْلِمٍ أَنْ يَتَوَالَى مَوْلَى رَجُلٍ مُسْلِمٍ بِغَيْرِ إِذْنِهِ ‏" ‏ ‏.‏ ثُمَّ أُخْبِرْتُ أَنَّهُ لَعَنَ فِي صَحِيفَتِهِ مَنْ فَعَلَ ذَلِكَ ‏.‏