Abu Hurayrah traced this back to the Prophet ﷺ, "Whoever catches one rakah of the prayer has caught the prayer."
حدثنا سفيان عن الزهري عن أبي سلمة
يبلغ به النبي ﷺ ومن أدرك من صلاة ركعة فقد أدرك
Its isnad is sahih. His saying "he traces it back"... he means that it is raised up to the Prophet ﷺ. Malik related it (10) from Zuhri, with this same isnad, with the wording, "he has caught up with the prayer." Bukhari (2:46-47) and Muslim (1:168-169) likewise related it, both by way of Malik. Muslim (1:169) also related it after that through many chains, among them the route of Sufyan bin Uyayna from Zuhri, which Ahmad related here. See what came before (7215), and what comes later (7529).