Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that the Messenger of Allah (peace and blessings be upon him) said: "Allah, the Mighty and Majestic, says: O son of Adam, as long as you call upon Me and place your hope in Me, I will forgive you, whatever may be in you. If you come to Me with sins filling the earth, and you do not associate anything with Me, I will meet you with forgiveness filling the earth. And if your sins reach the clouds of the sky, and then you seek My forgiveness, I will certainly forgive you."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12294