Hadith 25:300
Ubaydullah narrated to us, from Uthman ibn al-Aswad, from Mujahid and Ata, who both said: It is not permissible for a governor to buy from that which is under his authority. He said: And Mujahid said: Do not buy with one of your hands from the other.
حدثنا [ عبيد الله عن ] عثمان بن الأسود عن مجاهد وعطاء قالا لا يجوز لوال أن يشتري مما عليه قال وقال مجاهد لا تشتر إحدى يديك من الأخرى