Sunan Abi Dawud, Hadith 889 ⓘ
Ibn ‘Abbas reported the prophet as saying : I have been commanded, and sometimes the narrator said: Your prophet was commanded to prostrate on seven limbs.
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا شُعْبَةُ، عَنْ عَمْرِو بْنِ دِينَارٍ، عَنْ طَاوُسٍ، عَنِ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " أُمِرْتُ " . وَرُبَّمَا قَالَ أُمِرَ نَبِيُّكُمْ صلى الله عليه وسلم أَنْ يَسْجُدَ عَلَى سَبْعَةِ آرَابٍ .
also referenced under: Hadith 890 (DarusSalam) & Book 3, Hadith 889 (USC-MSA)