Musnad Ahmad 32:1493

Yahya ibn Ishaq narrated to us, he said: Hammad ibn Salamah informed me, from Qatadah, from Anas ibn Malik, "That the Messenger of Allah, peace and blessings of Allah be upon him, forbade *al-iq'a* (sitting on the buttocks with the thighs raised) and *al-tawarrud* (leaning to one side while sitting) in prayer." Abdullah said: "My father had abandoned this hadith."