فَاعْلَمْ أَنَّهُ لا إِلَهَ إِلا اللَّهُ وَاسْتَغْفِرْ لِذَنْبِكَ وَلِلْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ وَاللَّهُ يَعْلَمُ مُتَقَلَّبَكُمْ وَمَثْوَاكُمْ
Know, therefore, that there is no god but Allah, and seek forgiveness for your sin, and for the men and women who believe: for Allah knows how you move about and how you dwell in your homes.
This ayah is addressed to the Prophet Muhammad (saw). So at first glance it might seem to the reader to imply to the reader that he (saw) had committed some sin, since the ayah does say “Wastaghfir li dhanbik – And seek forgiveness for you sin”. But it is well-known and an agreed upon fact that the Prophet (saw), and indeed all the Prophets of Allah (as), were free from sin. This is part of our ‘aqidah as Muslims and no one disputes it. So why then was the Prophet (saw) commanded to seek forgiveness, seeing as he was free from sin? There are a number of explanations given for this and some of them are as follows:
It means that he should make istighfaar so that Allah (swt) would protect him from ever committing any sin. Another explanation is that the adress was made to him (saw) but what is intended is that it is meant for the Ummah. According to this interpretation it is an obligation on people to seek forgiveness for all of the Muslims. And it is also said that he (saw) was commanded to make istighfaar so that the rest of the Ummah would follow his example and also act upon this. Some were of the opinion that “li dhanbik – for your sin” means “li dhanbi ahli baitik – the sin of your household.” Yet another interpretation is that it was said to the Prophet (saw) and that the sin referred to is the abandonment of that which is most virtuous, which in relation to him (saw) is a sin (but not for other people). And there other explanations as well besides these.
And Allah (swt) knows best.