Musnad Ahmad 1153:2208

Yunus and Hassan ibn Musa narrated to us, they said: Hammad—meaning Ibn Salamah—narrated to us, from Ali ibn Zayd, from al-Hasan, that Umm Salamah—Hassan said: from Umm Salamah—she said: While the Messenger of Allah (peace and blessings of Allah be upon him) was lying down in my house, he suddenly sat up, saying: "To Allah we belong and to Him we shall return." I said: "May my father and mother be sacrificed for you, what is the matter with you, O Messenger of Allah, that you say 'To Allah we belong and to Him we shall return'?" He said: "An army from my nation will come from the direction of Ash-Sham, heading toward the House for a man whom Allah will protect from them. Until, when they are at al-Bayda’ in Dhu al-Hulayfah, they will be swallowed by the earth, even though their origins are diverse." I said: "O Messenger of Allah, how will they all be swallowed by the earth when their origins are diverse?" He said: "Among them are those who are coerced, among them are those who are coerced," three times.