It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Indeed, Allah, the Mighty and Majestic, says: 'Whoever among you knows that I have complete power to forgive sins, I forgive him, and I do not mind (the abundance of his sins), so long as he does not associate anything with Me.'" This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.