Jami` at-Tirmidhi 3339

Abu Hurairah narrated that :the Messenger of Allah said: “Al-Yawmul-Maw’ud (the Promised Day) is the Day of Resurrection, and Al-Yawmul-Mashhud (the Attended Day) is the Day of Arafah, and Ash-Shahid (the witness) is Friday.” He said: “The sun does not rise nor set, upon a day that is more virtuous than it. In it, there is an hour in which no believing worshipper makes a supplication to Allah for good, except that Allah answers it for him, and he does not seek Allah’s aid for something, except that He aids him in it.”