Sayyiduna al-Nawwas bin Sam'an (may Allah be pleased with him) says: I heard the Prophet (peace and blessings be upon him) saying: "Allah Almighty says: O son of Adam, do not fail to offer four rak'ahs in the early part of the day, and I will suffice you until the last part of it (the day)."
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are thiqat (trustworthy).