I said to Ibn Abbas, "Tell me about riding between Safa and Marwa, for your people claim that it is a sunnah."He replied, "They have spoken truly and they have spoken falsely."I asked, "What do you mean by 'they have spoken truly and they have spoken falsely'?"He said, "When the Messenger of Allah ﷺ arrived in Mecca, the people came out in such numbers that even the young women emerged from their homes. No one was struck aside to clear a path for the Messenger of Allah ﷺ. So the Messenger of Allah ﷺ mounted his ride and performed the going between Safa and Marwa while riding. Had he dismounted, walking would have been more beloved to him."
حدثنا يزيد أخبرنا الجريري
قلت لابن عباس حدثني عن الركوب بين الصفا والمروة فإن قومك يزعمون أنها سنة فقال صدقوا وكذبوا قلت ما صدقوا وكذبوا ماذا قال قدم رسول الله ﷺ مكة فخرجوا حتى خرجت العواتق وكان رسول الله ﷺ لا يضرب عنده أحد فركب رسول الله ﷺ فطاف وهو راكب ولو نزل لكان المشي أحب إليه
Its isnad is sahih. Jareeri is Saeed bin Iyas. The hadith is a repeat of 2843.