Musnad Ahmad 937:216

'Affan narrated to us, Hammam narrated to us, 'Amir al-Ahwal narrated to us, from Shahr ibn Hawshab, from Ma'di Karib, from Abu Dharr, from the Prophet (peace and blessings of Allah be upon him), in what he narrates from his Lord, the Almighty and Majestic, that He said: "O son of Adam, as long as you call upon Me and hope in Me, I will forgive you for what is in you, even if you were to meet Me with the earth full of sins, I would meet you with its equivalent in forgiveness. And if you were to commit sins until they reached the clouds of the sky, provided you did not associate anything with Me, and then you sought My forgiveness, I would forgive you, and I would not care."