Muwatta Malik · Hadith 371

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَسْتَتِرُ بِرَاحِلَتِهِ إِذَا صَلَّى ‏.‏

Yahya related to me from Malik that he had heard that Abdullah ibn Umar would use the animal he was riding as a sutra when he prayed

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).