Musannaf Ibn Abi Shayba 33:517

Hashim ibn al-Qasim narrated to us, he said: Abu Aqil narrated to us, he said: Isma'il ibn Abi Khalid narrated to us, he said: Abu al-Safar narrated to me, he said: Aisha said: "Indeed, the people have neglected the greatest part of their religion: piety (al-wara')."