Shu'bah (may Allah have mercy on him) relates: I asked al-Hakam (may Allah have mercy on him) about sitting cross-legged in prayer, and he described it as disliked (makruh) and said: I think Sayyiduna Ibn Abbas (may Allah be pleased with them both) also called it disliked.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3667