Sayyiduna Uqbah bin Amir (may Allah be pleased with him) says that one day, during the Battle of Tabuk, he went out with the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) was sitting and talking with his companions, and he (peace and blessings be upon him) said: "Whoever stands up when the sun has come in front of him, performs ablution well, then stands and offers two rak'ahs of prayer, (Allah Almighty) forgives his sins, and that person becomes as he was on the day his mother gave birth to him."
Abu Ya'la recorded it, and its chain contains a narrator whom I do not know.