Musnad Abu Ya'la al-Mawsili 107:30

Abu Khaythama narrated to us, Abdullah bin Yazid narrated to us, Haywah narrated to us, Abu Aqil narrated to us, from his cousin, from Uqbah bin Amir, that he went out with the Messenger of Allah (may Allah bless him and grant him peace) on the expedition of Tabuk. The Messenger of Allah (may Allah bless him and grant him peace) sat one day speaking to his companions, and he said: "Whoever stands when the sun faces him, then performs wudu and perfects his wudu, then stands and prays two rak'ahs, his sins will be forgiven, and he will be as he was the day his mother gave birth to him."