Musnad Abu Ya'la al-Mawsili 117:201

Abu Yasir Ammar bin Nasr narrated to us, Yusuf bin Atiyyah narrated to us, Thabit informed us, from Anas bin Malik, that the Prophet (peace be upon him) said: "The likeness of the believer is like the stalk of grain; it leans at times and stands straight at times. And the likeness of my nation is like the rain; it is not known whether its beginning is better or its end."