Musnad Ahmad 31:175

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, he said: I heard Zayd Abu al-Hawwari, he said: I heard Abu al-Siddiq narrating from Abu Sa‘id al-Khudri, he said: We feared that there would be an event after our Prophet, so we asked the Messenger of Allah, peace and blessings of Allah be upon him, and he said: "The Mahdi will emerge in my nation for five, or seven, or nine" — Zayd is the one who doubted — he said: We said: What thing? He said: "Years." Then he said: "The sky will send down upon them rain in abundance, and the earth will not withhold anything of its vegetation, and wealth will be piled up." He said: "A man will come to him and say: O Mahdi, give me, give me. He said: So he will heap up for him in his garment as much as he is able to carry."