To say Takbir while slaughtering
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.
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.