Sahih Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)
Book Number: 035 / Hadith Number: 6522
Al-Agharr al-Muzani, who was one amongst the Companions (of the Holy Prophet) reported that Allah's Messenger (may peace be upon him) said: There is (at times) some sort of shade upon my heart, and I seek forgiveness from Allah a hundred times a day.