Musnad Abu Ya'la al-Mawsili 209:59

Abdullah bin Mu'awiyah narrated to us, Hammad bin Salamah narrated to us, from Ali bin Zaid, from al-Hasan, from Umm Salamah, who said: While the Messenger of Allah (peace be upon him) was lying down in my house, he suddenly sat up while saying "Inna lillahi wa inna ilayhi raji'un" (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 that you say 'Inna lillahi wa inna ilayhi raji'un'?" He said: "For an army from my Ummah that will come from the direction of Ash-Sham, heading toward the House (the Ka'bah) 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: "May my father and mother be sacrificed for you, how will they be swallowed together while their origins are diverse?" He said: "Among them are those who are coerced, among them are those who are coerced, among them are those who are coerced."