O people, repent to Allah, for I repent to Him one hundred times a day

Everyone, regardless of his degree and level of faith, needs to return to Allah Almighty and perfect himself through repentance. No one is free from falling short in fulfilling the rights of Allah Almighty: {And turn to Allah in repentance all together, O believers}.
Repentance is general, whether it is for committing prohibited acts and sins or for falling short in performing obligatory duties.
Sincerity is a condition for the acceptance of repentance. Whoever abandons a sin for the sake of other than Allah is not considered repentant.
An-Nawawi said: Repentance has three conditions: to give up the sin, to regret doing it, and to be firmly determined not to return to such a sin ever. If the sin involves the right of another person, there is a fourth condition: to return what was wrongfully taken or to seek the forgiveness of the person wronged.
It is important to note that the Prophet's seeking forgiveness does not necessarily indicate that he committed sins. Rather, it reflects the perfection of his servitude and his constant connection to the remembrance of Allah Almighty, as well as his awareness of the greatness of Allah's rights and the shortcomings of a slave, no matter how much he does to thank Him for His blessings. It also serves as part of the legislation for the Ummah after him, among other rationales.