Musnad Ahmad 21:23

Ubayd ibn Abi Qurrah narrated to us, Layth ibn Sa’d narrated to us, from Abu Qubayl, from Abu Maysarah, from al-Abbas, who said: I was with the Prophet, peace and blessings of Allah be upon him, one night, and he said: "Look, do you see any star in the sky?" I said: "Yes." He said: "What do you see?" I said: "I see the Pleiades." He said: "As for it, there will follow this nation, equal to its number, from your loins, two during a tribulation."