Sahih Adab al-Mufrad

Sayyiduna Nu’man bin Bashir (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he said: “Supplication is worship.” Then he recited (this verse of the Qur’an): «ادعوني أستجب لكم» “Call upon Me; I will respond to you.”