It was narrated from ‘Aishah and Abu Hurairah that when the Messenger of Allah ﷺ wanted to offer a sacrifice, he brought two large, fat, horned, black-and-white, castrated rams. He slaughtered one on behalf of his nation, for whoever testified to Allah with monotheism and that he had conveyed (the Message), and he slaughtered the other on behalf of Muhammad and the family of Muhammad ﷺ. (Using translation from Ibn Mājah 3122)
أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا أَرَادَ أَنْ يُضَحِّيَ اشْتَرَى كَبْشَيْنِ عَظِيمَيْنِ سَمِينَيْنِ أَمْلَحَيْنِ أَقْرَنَيْنِ مَوْجَيَيْنِ فَيَذْبَحُ أَحَدَهُمَا عَنْ أُمَّتِهِ مِمَّنْ شَهِدَ بِالتَّوْحِيدِ وَشَهِدَ لَهُ بِالْبَلَاغِ وَذَبَحَ الْآخَرَ عَنْ مُحَمَّدٍ ﷺ وَآلِ مُحَمَّدٍ