Musnad Ahmad 1156:87

Ya'qub narrated to us, he said: My father narrated to me, from Ibn Ishaq, he said: Sulayman ibn Suhaym, the freed slave of the family of Jubayr, narrated to me, from Yahya ibn Abi Sufyan al-Akhnasi, from his mother, Umm Hakim bint Umayyah ibn al-Akhnas, from Umm Salamah, the wife of the Prophet, may Allah bless him and grant him peace, she said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "Whoever assumes the state of Ihram for an 'Umrah or a Hajj from al-Masjid al-Aqsa, his past sins will be forgiven." She said: So Umm Hakim rode [to travel] upon that hadith to Bayt al-Maqdis until she assumed the state of Ihram from there for an 'Umrah.