It was narrated from 'Aishah that:
a man bought a slave and put him to work, then he found some defect in him, so he returned him. He (the seller) said: "O Messenger of Allah he put my slave to work." The Messenger of Allah ﷺ said: "A slave's earnings belong to his guarantor."

حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا مُسْلِمُ بْنُ خَالِدٍ الزَّنْجِيُّ، حَدَّثَنَا هِشَامُ بْنُ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ رَجُلاً، اشْتَرَى عَبْدًا فَاسْتَغَلَّهُ ثُمَّ وَجَدَ بِهِ عَيْبًا فَرَدَّهُ . فَقَالَ يَا رَسُولَ اللَّهِ إِنَّهُ قَدِ اسْتَغَلَّ غُلاَمِي . فَقَالَ رَسُولُ اللَّهِ ﷺ " الْخَرَاجُ بِالضَّمَانِ " .