Musnad Ahmad 27:1583

Sulayman ibn Dawud narrated to us, Ibrahim ibn Sa'd informed us, from al-Zuhri; and Ya'qub said: My father narrated to us, he said: Ibn Shihab narrated to us, from Salim ibn 'Abd Allah, from 'Abd Allah, from the Messenger of Allah (may Allah bless him and grant him peace) that he said: "The keys of the Unseen are 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]