Language:
كتاب الأضاحي
73  
Al-Adha Festival Sacrifice (Adaahi)
(14)
Chapter: To say Takbir while slaughtering
(14)
باب التَّكْبِيرِ عِنْدَ الذَّبْحِ
Sahih al-Bukhari 5565

Narrated Anas:

The Prophet (ﷺ) offered as sacrifices, two horned rams, black and white in color. He slaughtered them with his own hands and mentioned Allah's Name over them and said Takbir and put his foot on their sides.

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ ضَحَّى النَّبِيُّ صلى الله عليه وسلم بِكَبْشَيْنِ أَمْلَحَيْنِ أَقْرَنَيْنِ، ذَبَحَهُمَا بِيَدِهِ، وَسَمَّى وَكَبَّرَ وَوَضَعَ رِجْلَهُ عَلَى صِفَاحِهِمَا‏.‏
Reference : Sahih al-Bukhari 5565
In-book reference : Book 73, Hadith 21
USC-MSA web (English) reference : Vol. 7, Book 68, Hadith 472
  (deprecated numbering scheme)