ENOfficial
It was narrated from Az-Zuhri concerning two slaves who were partners, and one of them quit, that he said: "One of them may cover for the other if they were partners."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ أَنْبَأَنَا ابْنُ الْمُبَارَكِ، عَنْ يُونُسَ، عَنِ الزُّهْرِيِّ، فِي عَبْدَيْنِ مُتَفَاوِضَيْنِ كَاتَبَ أَحَدُهُمَا قَالَ جَائِزٌ إِذَا كَانَا مُتَفَاوِضَيْنِ يَقْضِي أَحَدُهُمَا عَنِ الآخَرِ.
sunnah.com