Musnad Ahmad 27:684

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from 'Abdullah ibn Dinar, from Ibn 'Umar, from the Prophet, peace and blessings of Allah be upon him, who said: "The keys of the unseen are five; none knows them except Allah: No one knows what is in tomorrow except Allah, and no one knows the descent of rain except Allah, and no one knows what is in the wombs except Allah, and no one knows the Hour except Allah. And no soul knows what it will earn tomorrow, and no soul knows in what land it will die."