Ibn Umar was on a journey when a companion of his dismounted to perform the witr prayer.Ibn Umar asked, "What is the matter with you? Why don't you ride?"He replied, "I am performing witr."Ibn Umar said, "Do you not have in the Messenger of Allah ﷺ an excellent example?"
حدثنا عبد الله بن الحارث حدثني داود بن قيس عن نافع
أنه كان في سفر فنزل صاحب له يوتر فقال ابن عمر ما شأنك لا تركب قال أوتر قال ابن عمر أليس لك في رسول الله ﷺ أسوة حسنة
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Its isnad is sahih, and something similar in meaning has already been mentioned several times, most recently at 6224. It seems clear that this companion of Ibn Umar, the one who dismounted to pray witr, is Saeed bin Yasar, since his hadith has already appeared at 5208 and 5209, where Ibn Umar said to him, "Do you not have the example of the Messenger of Allah ﷺ? The Messenger of Allah ﷺ used to pray witr while riding his camel." See also Muwatta 1:145.