It is narrated from Sayyiduna Mu'adh bin Anas al-Juhani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever remains sitting in his place of prayer after praying the Fajr prayer until he prays the Duha (forenoon) prayer, and says nothing but good, his sins are forgiven, even if they are more than the foam of the sea."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17576