Musnad Ahmad 27:1130

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Umar ibn Muhammad ibn Zayd, that he heard his father, Muhammad, narrating from Ibn ‘Umar, from the Prophet, peace and blessings of Allah be upon him, who said: "I have been given the keys to everything except the five: 'Indeed, Allah [alone] has knowledge of the Hour and sends down the rain and knows what is in the wombs, and no soul perceives what it will earn tomorrow, and no soul perceives in what land it will die. Indeed, Allah is Knowing and Acquainted.'" [Luqman: 34]