No one has narrated more hadith from the Messenger of Allah ﷺ than I have, except Abdullah bin Amr, for he used to write them down while I did not.
حدثنا سفيان عن عمرو عن ابن منبه يعني وهبا عن أخيه سمعت
ليس أحد أكثر حديثا عن رسول الله ﷺ مني إلا عبد الله بن عمرو فإنه كان يكتب وكنت لا أكتب
Its chain of transmission is sahih. Wahb bin Munabbi, his reliability was already established at 2967. "From his brother" means Hammam bin Munabbih, who is a well known trustworthy taabii. Bukhari mentioned him in al-Kabir 4/2/236 and al-Saghir 155, and Ibn Saad in al-Tabaqat 5:396.Bukhari related this hadith at 1:184, from Ibn Madini, from Sufyan bin Uyayna, with this same chain, but Muslim did not include it, as the Hafiz stated at the end of the Book of Knowledge in al-Fath 1:204.See also what came before in the Musnad of Abdullah bin Amr bin As, at 6510, 6802, 6930, 7018, and 7020.