Musnad Ahmad 1153:1094

Sulayman ibn Dawud al-Hashimi narrated to us, Ibrahim—meaning Ibn Sa’d—informed us, from al-Zuhri, from ‘Urwah, from ‘Aishah, who said: I said: "Have you considered the saying of Allah, the Almighty and Majestic: 'Indeed, as-Safa and al-Marwah are among the symbols of Allah. So whoever makes Hajj to the House or performs ‘Umrah, there is no blame upon him for walking between them' [Al-Baqarah: 158]?" She said: I said: "By Allah, there is no blame upon anyone if he does not walk between them." She said: ‘Aishah said: "How evil is what you have said, O son of my sister! If it were as you interpreted it, it would have been: 'There is no blame upon him if he does not walk between them.' However, it was only revealed because the Ansar, before they embraced Islam, used to enter into the state of Ihram for Manat, the idol which they used to worship at al-Mushallal. Whoever entered into Ihram for it used to feel it sinful to walk between as-Safa and al-Marwah." "So they asked the Messenger of Allah, peace and blessings of Allah be upon him, about that and said: 'O Messenger of Allah, we used to feel it sinful to walk between as-Safa and al-Marwah during the Jahiliyyah.' Then Allah, the Almighty and Majestic, revealed: 'Indeed, as-Safa and al-Marwah are among the symbols of Allah,' up to His saying: 'there is no blame upon him for walking between them.'" ‘Aishah said: "Then the Messenger of Allah, peace and blessings of Allah be upon him, established the Sunnah of walking between them, so it is not appropriate for anyone to abandon walking between them."