Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "Indeed, Allah Almighty says: O son of Adam, offer four rak'ahs for Me in the early part of the day, and because of them I will suffice you until the last part of the day."
Ahmad and Abu Ya'la recorded it, and its narrators are thiqat (trustworthy).