Musnad Ahmad 26:882

Muhammad ibn Ja‘far narrated to us, Sa‘id ibn Abi ‘Arubah narrated to us, from Qatadah, from Abu al-Ahwas, from Ibn Mas‘ud: "The Messenger of Allah, may Allah bless him and grant him peace, used to prefer the prayer of the congregation over the prayer of a man alone by twenty-five times, all of them like his prayer."