مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4195
Musnad of Abdullah bin Mas'ood
Abu ‘Amr ash-Shaibani said: The owner of this house - meaning Ibn Mas'ood - told me: I said: O Messenger of Allah, which deed is best? He said: "Prayer offered on time.”
Musnad Ahmad 4223Its isnad is saheeh]