Musnad Ahmad 456:26

Abu Amir narrated to us, Hisham—meaning Ibn Sa'd—narrated to us, from Zayd—meaning Ibn Aslam—from 'Ata' ibn Yasar, from Zayd ibn Khalid al-Juhani, that the Prophet (peace and blessings of Allah be upon him) said: "Whoever performs ablution and perfects his ablution, then prays two rak'ahs in which he does not become heedless, Allah will forgive him his past sins."