Regarding two slaves who are partners in a mufawadah partnership, where one of them concludes a kitabah contract, he said, "It is permissible, since they are partners in mufawadah, and one of them may settle obligations on behalf of the other."
أخبرنا علي بن حجر قال أنبأنا ابن المبارك عن يونس
في عبدين متفاوضين كاتب أحدهما قال جائز إذا كانا متفاوضين يقضي أحدهما عن الآخر
No references are available.
[Its chain of transmission is sahih] Nasai alone narrated it.