He reported that he used to see Abdullah bin Umar sitting cross-legged during prayer. He said, "I did the same, as I was young at the time, but Abdullah forbade me and said, 'The sunnah of prayer is that you keep your right foot upright and fold your left leg beneath you.'"I said to him, "But you yourself do this."He replied, "My legs cannot bear my weight."
أنه أخبره أنه كان يرى عبد الله بن عمر يتربع في الصلاة إذا جلس، قال: ففعلته وأنا يومئذ حديث السن، فنهاني عبد الله، وقال: إنما سنة الصلاة أن تنصب رجلك اليمنى، وتثني رجلك اليسرى، فقلت له: فإنك تفعل ذلك. فقال: إن رجلي لا تحملاني.
Malik narrated it in his chapter on prayer (51) from Abdul-Rahman bin Qasim, from Abdullah bin Abdullah bin Umar, mentioning something similar. Bukhari narrated it in his chapter on the adhan (827) from Abdullah bin Maslama, from Malik, with the same wording. In the version of Nasai (1157) and Abu Dawud (959), by way of Yahya bin Saeed, from Qasim bin Muhammad, from Abdullah bin Umar, from his father, he said, "Part of the sunnah of prayer is that you lay down your left leg and keep the right one upright." Laying down here means sitting cross-legged (iftirash). It appears from this that Abdul-Rahman bin Qasim bin Muhammad and his father Qasim bin Muhammad both narrated from Abdullah bin Abdullah bin Umar, and in some versions Abdul-Rahman bin Qasim narrates from his father, from Abdullah bin Abdullah bin Umar, and all of them are sahih.Malik also narrated, from Yahya bin Saeed, that Qasim bin Muhammad showed them the sitting position for the tashahhud. He kept his right leg upright, folded his left leg, and sat on his left hip, not sitting on his foot, then he said, "Abdullah bin Abdullah bin Umar showed me this, and he told me that his father used to do it."Amr bin Harith also narrated it, from Yahya, that Qasim told him, from Abdullah bin Abdullah bin Umar, from his father, who said, "Part of the sunnah of prayer is that you keep the right foot upright, with its toes facing the qibla, and sit on the left one." Nasai narrated it (1158) from Rabi bin Sulayman bin Dawud, who said, Ishaq bin Bakr bin Mudar narrated to us, who said, my father narrated to me, from Amr bin Harith, and mentioned it.