Reference: Siyar A’laam an-Nubalaa – Volume 14, Page 36
Muhammad ibn Ya’qoob al-Akhram said:
I have not seen any better prayer than that of Muhammad ibn Nasr. A house fly settled upon his ear, and he did not [even] try to brush it away. And we were amazed at the gracefulness of his prayer, and his concentration and state; He would place his chin upon his chest and then stand upright as if he was an erect piece of wood.