He heard Jabir being asked whether the Prophet ﷺ took the pledge of allegiance at Dhul Hulayfah.Jabir answered, "No, but he prayed there. He only took the pledge under the tree at Hudaybiyah, that specific tree."He also informed us that he heard Jabir supplicate at the well of Hudaybiyah.
حدثنا حجاج قال ابن جريج
أنه سمع جابرا يسأل هل بايع النبي ﷺ بذي الحليفة قال لا ولكن صلى بها ولم يبايع عند الشجرة إلا الشجرة التي للحديبية و أخبرنا أنه سمع جابرا دعا على بئر الحديبية
Its isnad is sahih, and Ahmad alone narrated it, as far as I know.