Musnad Ahmad 33:891

Hammad al-Khayyat narrated to us, Asim ibn Umar narrated to us, from Asim ibn Ubayd Allah, from Abdullah ibn Amir ibn Rabiah, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever spends a day in the state of Ihram, reciting the Talbiyah, until the sun sets, his sins set just as the day he was born of his mother."