Narrated Anas:

The Prophet (ﷺ) sacrificed two horned rams which were white with black markings, slaughtered, and uttered: "Allah is Most Great." and mentioned Allah's name and placed his foot on their sides.

حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا هِشَامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم ضَحَّى بِكَبْشَيْنِ أَقْرَنَيْنِ أَمْلَحَيْنِ يَذْبَحُ وَيُكَبِّرُ وَيُسَمِّي وَيَضَعُ رِجْلَهُ عَلَى صَفْحَتِهِمَا ‏.‏