Sunan an-Nasa'i, Volume 5, Book 43, Hadith 4421 (DarusSalam) ⓘ
Anas bin Malik said: "The Messenger of Allah used to sacrifice two pronounce the name of Allah and say: 'Allah Akabar,' and I saw him slaughtering them with his own hand, and placing his foot on their sides "(Sahih )
أَخْبَرَنَا أَحْمَدُ بْنُ نَاصِحٍ، قَالَ حَدَّثَنَا هُشَيْمٌ، عَنْ شُعْبَةَ، عَنْ قَتَادَةَ، قَالَ حَدَّثَنَا أَنَسُ بْنُ مَالِكٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُضَحِّي بِكَبْشَيْنِ أَمْلَحَيْنِ أَقْرَنَيْنِ وَكَانَ يُسَمِّي وَيُكَبِّرُ وَلَقَدْ رَأَيْتُهُ يَذْبَحُهُمَا بِيَدِهِ وَاضِعًا رِجْلَهُ عَلَى صِفَاحِهِمَا .
also referenced under: Hadith 4416 (Reference) & Book 43, Hadith 56 (In-Book)