Musannaf Ibn Abi Shaybah 4718 — A man praying while sitting in ihtiba

The father of al-Hasan bin Amr said: I saw Sa'id bin Jubayr praying sitting in ihtiba'. When he was about to bow, he would undo his ihtiba', then stand up and bow. (Ihtiba' means that a person sits on his buttocks with his knees raised and clasps his hands around them for support, or ties a cloth around his back and knees. The Arabs often used to sit in this way.)