I saw Ibn Umar pass by a man who had made his mount kneel down and was about to slaughter it. He said, "Have it standing with its leg tied. That is the sunnah of the Messenger of Allah ﷺ."
حدثنا محمد بن جعفر حدثنا شعبة عن يونس بن عبيد
رأيت ابن عمر مر برجل قد أناخ مطيته وهو يريد أن ينحرها فقال قياما مقيدة سنة رسول الله ﷺ
Its isnad is sahih, and it is a repetition of 4459. In a copy noted in the margin of M, "his mount" is written as "his sacrificial animal."