Musnad Ahmad 9:23

Hammad ibn Usamah narrated to us, Mis'ar informed me, from 'Abd al-Malik ibn Maysarah, from Hilal ibn Yasaf, from 'Abdullah ibn Zalim, from Sa'id ibn Zayd, who said: The Messenger of Allah, peace and blessings of Allah be upon him, mentioned tribulations like pieces of the dark night. I believe he said: "People may perish in them, the fastest of perishing." It was said: "Will all of them perish, or some of them?" He said: "Killing is sufficient for them—or, it is sufficient for them."