The iqamah for the dawn prayer was called, and a man stood up to pray the two voluntary units. The Messenger of Allah ﷺ pulled him by his garment and said, "Are you praying the dawn prayer as four units?"
أقيمت صلاة الصبح، فقام رجل يصلي الركعتين، فجذب رسول الله ﷺ بثوبه فقال: أتصلي الصبح أربعا؟
Imam Ahmad narrated it (2130) from Yazid, who said, Salih bin Rustum Abu Amir told us, from Abdullah bin Abu Mulayka, from Ibn Abbas, and he mentioned something similar. He also narrated it (3329) from Waki, from Salih bin Rustum with the same chain, and its wording was, "The prayer was called for, and I had not yet prayed the two rakahs, and he saw me praying them, so he pulled me and said, 'Do you want to pray the dawn prayer as four rakahs?'" It was said to Ibn Abbas, "From the Prophet ﷺ?" He said, "Yes." From this it becomes clear that the one who was praying the two rakahs of Fajr after the call to prayer had been given was Ibn Abbas himself. Abu Yaala also narrated something similar (2568), as did Ibn Khuzayma in his Sahih (1124), and Hakim (1/307), all of them through various routes from Waki with the same chain and similar wording.Ibn Hibban also narrated it (2469) in his Sahih through another route from Abu Amir Khazzaz, who is Salih bin Rustum, with the same account. Its isnad is hasan, for although Salih bin Rustum is among the narrators of Muslim, there is disagreement about him, and the conclusion is that his hadith is hasan.Yahya bin Saeed Qattan alone narrated it differently, reporting it from Abu Amir Khazzaz, from Abu Yazid, from Ikrima, from Ibn Abbas, that the Prophet ﷺ entered the masjid for the morning prayer and found a man praying the two rakahs of Fajr, and he mentioned the hadith. Bazzar narrated this in Kashf Astar (518) from Ibrahim bin Muhammad Taymi, who said, Yahya bin Saeed Qattan told us, and he related it.Bazzar said, "Some of them narrated it from Ibn Abu Mulayka, from Ibn Abbas, and we do not know of anyone who narrated it with this isnad except Yahya, from Abu Amir."I say, it does no harm that Yahya bin Saeed narrated it alone, for he is trustworthy and a hafiz, and the teacher of his teacher, namely Abu Yazid, was a man of Madinah who lived in Basra. His name is not known, but he became well known by his kunya. Ibn Main deemed him trustworthy, and Bukhari narrated from him. One who is known is proof against one who is not known.