The Messenger of Allah ﷺ used to perform voluntary prayer while riding his mount, not concerning himself with the direction it faced, indicating the prostrations with a nod of his head. Ibn Umar used to do the same.
حدثنا عصام بن خالد حدثنا شعيب بن أبي حمزة وأبو اليمان قال أخبرنا شعيب بن أبي حمزة عن الزهري حدثني سالم بن عبد الله
أن رسول الله ﷺ كان يسبح وهو على ظهر راحلته لا يبالي حيث كان وجهه ويومئ برأسه إيماء وكان ابن عمر يفعل ذلك
Its isnad is sahih. Ahmad reported it from two teachers, Isam bin Khalid and Abu Yaman, both from Shuayb bin Abu Hamza.Isam bin Khalid Hadrami, his reliability was established earlier at 1464, and we add here that Bukhari gave his biography in al-Kabir 21/1/4, and Ibn Abu Hatim in al-Jarh wal-Tadil 26/2/3, where he said, "Ahmad bin Hanbal reported from him. I heard my father say that." His name appears in the three manuscripts at this place as Asim bin Khalid, which is certainly an error beyond doubt, for there is no one among the teachers of Ahmad named Asim bin Khalid, nor indeed among the transmitters whose biographies have been recorded is there anyone by that name. For this reason we determined decisively that it is an error, and we have recorded here the correct form, about which there is no doubt, even though it contradicts the three manuscripts.As for the hadith, Bukhari reported something of similar meaning at 473 and 474, by way of Abdul-Aziz bin Muslim, from Abdullah bin Dinar, from Ibn Umar, and also by the route of Layth, from Yunus, from Zuhri, from Salim, from his father. Something of similar meaning has also passed earlier by the route of Musa bin Uqba, from Salim, from his father, at 5822. See also 6071 and 6120.His statement, "he performs tasbih," means he performs the voluntary prayer, as was explained earlier at 5185.His statement, "Salim bin Abdullah," the words "bin Abdullah" were not mentioned in manuscript K, but were recorded in its margin as an alternate reading.His statement, "wherever his face was turned," this is what appears in manuscripts H and M, while in manuscript K it reads, "wherever he turned," and what appears here was noted as an alternate reading in its margin.