Scholars said: It is necessary to repent from every sin. If the offense involves the Right of Allah, not a human, then there are three condition to be met in order that repentance be accepted by Allah:
1- To desist from committing it.
2- To feel sorry for committing it.
3- To decide not to recommit it.
Any repentance failing to meet any of these three conditions, would not be sound.
But if the sin involves a humans right, it requires a fourth condition, i.e., to absolve onself from such right. If it is a property, he should return it to its rightful owner. If it is slandering or backbiting, one should ask the pardon of the offended.
One should also repent from all sins. If he repents from some, his repentance would still be sound according to the people of sound knowledge. He should, however, repent from the rest. Scriptural proofs from the Book and the Sunnah and the consensus of the scholars support the incumbency of repentance.
Allah, the, Exalted says:
"And all of you beg Allah to forgive you, O believers, that you may be successful". (24:31)
"Seek the forgiveness of your Rubb, and turn to Him in repentance". (11:3)
"O you who believe! Turn to Allah with sincere repentance!". (66:8)