Abu Hurayrah (may Allah be pleased with him) reported that he heard the Prophet (may Allah's peace and blessings be upon him) say: "By Allah! I ask Allah for forgiveness and repent to Him more than seventy times a day."
The Prophet (may Allah's peace and blessings be upon him), whose past and future sins had been forgiven by Allah, swore that he would seek Allah's forgiveness and repent to Him over seventy times every day. The Prophet's pursuit of forgiveness was not necessarily for sins that he had committed, but it was part of his complete servitude to Allah, deep attachment to His remembrance, and the feeling of the tremendous duty towards Him and the shortcoming of His servants no matter how much they show gratitude. His act does also serve the purpose of prescribing the religious deeds for the Ummah.