Musannaf Ibn Abi Shayba 33:90

Abu Khalid al-Ahmar narrated to us, from ‘Amr ibn Qays, from ‘Amr ibn Murrah, from ‘Abdullah ibn Mas‘ud, who said: The Messenger of Allah (may Allah bless him and grant him peace) recited: "Whoever Allah wills to guide, He expands his chest for Islam." They said: "O Messenger of Allah, what is this expansion?" He said: "A light which is cast into the heart, so the heart expands for it." It was said: "Is there a sign by which that is known?" He said: "Yes." It was said: "And what is it?" He said: "Turning towards the abode of eternity, distancing oneself from the abode of deception, and preparing for death before the arrival of death."