The cure for sins is seeking forgiveness from Allah the Mighty and Majestic

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) urinated while standing, and some drops of his urine splashed onto his shins and feet. A man said to him: "Drops of your urine have got onto your feet and shins." He gave him no reply until he reached the house of some people and asked them for water for ablution. They brought out water, so he performed ablution and washed his shins and feet. Then he turned to that man and asked: "What did you say?" He said: "Now you have done it (by washing)." Sayyiduna Abu Dharr (may Allah be pleased with him) said: "This is the remedy for this (outward impurity), and the remedy for sins is that you seek forgiveness from Allah, the Mighty and Majestic."
Although this report is mawquf (a Companion's statement), its chain from Sayyiduna Anas to Sayyiduna Abu Dharr (may Allah be pleased with them both) is sahih (authentic), and this is its (proper) place.

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "A servant committed a sin and said: 'O my Lord, I have committed a sin, so forgive me.' His Lord said: 'My servant knows that he has a Lord who forgives sin and also takes to account for it.' So Allah forgave him. Then he refrained (from sins) for as long as Allah willed, then he committed another sin and said: 'O my Lord, I have committed a sin, so forgive me.' His Lord, the Mighty and Majestic, said: 'My servant knows that he has a Lord who forgives sin and also takes to account for it. I have forgiven My servant, so let him do what he wishes.' Then he sinned a third time and said: 'Lord, forgive me my sin.' Allah, Glorified and Exalted, said: 'My servant committed a sin and he knows that he has a Lord who forgives sin and also takes to account for sin. (O servant,) do what you wish, I have forgiven you.'"
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), and they did not record it.

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever commits a sin and knows that he has a Lord who, if He wishes, will forgive him and, if He wishes, will punish him, it is a right upon Allah Almighty (out of His generosity) that He forgive him."
This hadith has a sahih (authentic) chain, and they (the two Shaykhs) did not record it.