Musnad Ahmad 2:306

Waki’ narrated to us, from Isra’il, from Abu Ishaq, from ‘Amr ibn Maymun, from ‘Umar: That the Prophet, peace and blessings of Allah be upon him, used to seek refuge from stinginess, cowardice, the punishment of the grave, the vilest of old age, and the trial of the chest. Waki’ said: The trial of the chest is that a man dies, and Waki’ mentioned the trial [as being] that he did not repent from it.