Sahih al-Bukhari, Volume 9, Book 93, Hadith 496 (USC-MSA) ⓘ
Narrated Anas: The Prophet slaughtered two rams as sacrifice and mentioned Allah's Name and said, "Allahu-Akbar" while slaughtering).
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، حَدَّثَنَا هِشَامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ ضَحَّى النَّبِيُّ صلى الله عليه وسلم بِكَبْشَيْنِ، يُسَمِّي وَيُكَبِّرُ.
also referenced under: Book 97, Hadith 28 (In-Book) & Hadith 7399 (DarusSalam)