Musnad Ahmad 2:40

Abdullah ibn Yazid narrated to us, Haywah narrated to us, Abu Aqil informed us, from his cousin, from Uqbah ibn Amir, that he went out with the Messenger of Allah, may Allah bless him and grant him peace, on the expedition of Tabuk. One day, the Messenger of Allah, may Allah bless him and grant him peace, sat down to speak to his companions and said: "Whoever stands when the sun has passed its zenith, then performs ablution and perfects the ablution, then stands and prays two rak'ahs, his sins will be forgiven for him, and he will be as he was on the day his mother gave birth to him." Uqbah ibn Amir said: I said, "Praise be to Allah who has granted me the provision of hearing this from the Messenger of Allah, may Allah bless him and grant him peace." Umar ibn al-Khattab, who was sitting opposite me, said to me: "Are you amazed by this? The Messenger of Allah, may Allah bless him and grant him peace, said something more amazing than this before you arrived." I said: "And what is that, may my father and mother be sacrificed for you?" Umar said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Whoever performs ablution and perfects the ablution, then raises his gaze to the sky and says: 'I bear witness that there is no god but Allah alone, with no partner, and I bear witness that Muhammad is His servant and His messenger,' the eight gates of Paradise will be opened for him, and he may enter through whichever of them he wishes."