we asked Ibn ‘Abbas about sitting on heels between the two prostrations. He said: It is the sunnah. We said: We look upon it as a pressure on the foot. He said: This is the sunnah of your Prophet ﷺ (Using translation from Abū Dāʾūd 845)
أَنَّهُ سَمِعَ طَاوُسًا يَقُولُ قُلْنَا لِابْنِ عَبَّاسٍ فِي الْإِقْعَاءِ عَلَى الْقَدَمَيْنِ؟ فَقَالَ هِيَ السُّنَّةُ قَالَ فَقُلْنَا إِنَّا لَنَرَاهُ جَفَاءً بِالرِّجْلِ فَقَالَ ابْنُ عَبَّاسٍ هِيَ سُنَّةُ نَبِيِّكَ ﷺ