Reference: Siyar A’laam an-Nubalaa – Volume 17, Page 646
al-Qaasim ibn ‘Asaakir reported on the authority of Sulaym ibn Ayyoob:
About him, I was told he would take account of himself [to the level of every] breath; he would not let time pass without [utilising it for] benefit. He would be [busy] either writing, teaching, or reading. I was told he would even be moving his lips when sharpening his pen[cil].