Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) used to sacrifice two fine black-and-white rams. When he intended to slaughter, he would place his foot on their sides and say: "In the name of Allah; this is from You and for You. O Allah, accept it from Muhammad (peace and blessings be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11281