Musnad Ahmad 1067:0

Narrated to us by Muhammad ibn Ja’far, who said: Narrated to us by Shu’bah, from Muhammad ibn al-Munkadir, who said: I heard Muhammad ibn al-Munkadir say: I heard Jabir ibn ‘Abdullah say: The Messenger of Allah (ﷺ) said: "The keys to Paradise are prayer, and the key to prayer is purification."