It is narrated from Hazrat Abu Dharr Ghifari (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: Allah Almighty says, "O My servant! However much you worship Me and place your hope in Me, I will forgive all your sins. O My servant! If you come to Me with sins as much as the earth but do not associate anyone with Me, I will meet you with as much forgiveness, and it will not matter to Me." ... Then the narrator mentioned the entire hadith.
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 21505
Hadith Gradingحکم دارالسلام:حديث حسن، م: 2687، وهذا إسناد ضعيف، شهر بن حوشب ضعيف، وقد اختلف عليه فى الحديث، ومعدي كرب مجهول