Musnad Abu Ya'la al-Mawsili 209:22

Abu Bakr narrated to us, Abd al-A’la ibn Abd al-A’la narrated to us, from Muhammad ibn Ishaq, who said: Sulayman ibn Suhaym narrated to me, from Umm Hakim bint Umayyah, from Umm Salamah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever enters into the state of Ihram for an Umrah from Bayt al-Maqdis (Jerusalem), his [past] sins will be forgiven."