"We asked Ibn Abbas about squatting (sitting) on the heels. He said: 'It is the Sunnah.' We said: 'We think that it is difficult for a man.' He said: 'Rather, it is Sunnah of your Prophet.'"  

أَنَّهُ سَمِعَ طَاوُسًا يَقُولُ قُلْنَا لاِبْنِ عَبَّاسٍ فِي الإِقْعَاءِ عَلَى الْقَدَمَيْنِ قَالَ هِيَ السُّنَّةُ فَقُلْنَا إِنَّا لَنَرَاهُ جَفَاءً بِالرَّجُلِ قَالَ بَلْ هِيَ سُنَّةُ نَبِيِّكُمْ ﷺ