Abdullah bin Amir narrated that Sayyiduna Abu Umamah and Sayyiduna Utbah bin Abd al-Sulami (may Allah be pleased with them both) told him that the Messenger of Allah (peace and blessings be upon him) said: "Whoever prays the Fajr prayer in congregation, then remains in the mosque until he prays the voluntary Duha prayer, will have a reward like that of one performing Hajj and Umrah, his Hajj and Umrah complete."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14389