(a) Humayd al-Tawil (may Allah have mercy on him) narrates: I saw Bakr bin Abdullah (may Allah have mercy on him) praying cross-legged while leaning for support.
(b) It is reported from Mujahid (may Allah have mercy on him) and Ibrahim al-Nakha'i (may Allah have mercy on him), concerning a sick person, that he may pray sitting cross-legged.
(c) It has been narrated to us that Umar bin Abd al-Aziz (may Allah have mercy on him) also did so, and it is reported from Ibn Abbas (may Allah be pleased with them both) that he regarded it as disliked.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3666