Ishaq bin Sa'id bin Amr bin Sa'id bin al-As (may Allah have mercy on him) said: My father narrated to me from his father, who said: I was with Sayyiduna Uthman bin Affan (may Allah be pleased with him). He called for water for ablution and said: I was present with the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "When a Muslim servant performs ablution well and attends an obligatory prayer, then performs its bowing and prostration well too, then if he avoids the major sins, his minor sins are forgiven; and this is so for all time." [Sahih. Muslim]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20757