Musnad Ahmad 1153:328

Waki’ narrated to us, he said: Ja’far ibn Burqan narrated to us, from ‘Abdullah al-Bahī, from ‘Aishah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, whoever is gentle with my Ummah, then be gentle with him, and whoever is harsh upon them, then be harsh upon him."