It is narrated from Sayyiduna al-Irbad bin Sariyah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever performs an obligatory prayer has one supplication that will be answered, and whoever completes the Qur'an also has one supplication that will be answered."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15738