Sayyiduna Nu'aym bin Hammar al-Ghatafani (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that Allah Almighty says: "O son of Adam, pray four rak'ahs for Me at the beginning of the day, and I will suffice you until its end."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4901