Musnad Ahmad 32:269

Waki' narrated to us, Hisham narrated to us, Qatadah narrated to us, from Anas ibn Malik, who said: I shall narrate to you a hadith that I heard from the Messenger of Allah, may Allah bless him and grant him peace, which no one will narrate to you after me. I heard him saying: "The Hour will not be established until there is one guardian for fifty women, and women become numerous, and men become few."