Musnad Ahmad 26:617

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Amr ibn Murrah, who said: I heard ‘Abdullah ibn Salamah saying: I heard ‘Abdullah ibn Mas‘ud saying: "Your Prophet, may Allah bless him and grant him peace, was 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]." He said: I said to him: "Did you hear it from ‘Abdullah [ibn Mas‘ud]?" He said: "Yes, more than fifty times."