Musnad Abu Ya'la al-Mawsili 2:110

Zuhayr ibn Harb narrated to us, Abdullah ibn Yazid narrated to us, Haywah informed us, Abu Aqil informed us, from his cousin, from Uqbah ibn Amir al-Juhani, 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 his ablution, then stands and prays two rak'ahs, his sins will be forgiven," or he said, "He will be as he was the day his mother gave birth to him." Uqbah 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: "Are you amazed by this? For the Messenger of Allah (may Allah bless him and grant him peace) said something more amazing than this before you arrived." I said: "May my father be sacrificed for you, what did he say?" Umar ibn al-Khattab said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever performs ablution and perfects the ablution, then raises his sight 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; he may enter through whichever of them he wishes."