Shaykh Mufti Muhammad Rafi` Usmani (may Allah preserve him) states:

In the Noble Qur’an, the command for repentance has been given as such:
تُوبُوا إِلَى  اللَّهِ جَمِيعًا أَيُّهَ الْمُؤْمِنُونَ لَعَلَّكُمْ تُفْلِحُونَ 

Turn to Allah in repentance, all of you, O believers, that you might succeed. (Surah Nur, Verse 31)

Each one of us is involved in some sin or another, as no one is free from sins. Some of us, however, commit more sins and some of us less. From all people, though, the best are those who repent. Therefore, when a sin is committed, keep the requirements of repentance in mind and immediately repent.

In Surah Tahrim, Allah Most High says:

يَا أَيُّهَا الَّذِينَ  آمَنُوا تُوبُوا إِلَى اللَّهِ  تَوْبَةً نَّصُوحًا

O you who believe, repent to Allah with a sincere and firm repentance (Surah Tahrim, Verse 8

This verse refers to a repentance that is both sincere and has firmness. Therefore, we can see that, despite being innocent and protected from sin, the Holy Prophet (Allah bless him and grant him peace) used to seek forgiveness from Allah more than 70 times in a day (as mentioned in a Hadith.)

Now, the question comes to mind: If the Holy Prophet (Allah bless him and grant him peace) did not sin, then from what did he repent? Understand that there are two aspects to this:

One purpose was to set an example for the Ummah. If the most beloved creation to Allah and such an exalted messenger used to seek Allah’s forgiveness more than 70 times a day, then we should do even more than that.

The Holy Prophet (Allah bless him and grant him peace) did not seek forgiveness due to sins. His good deeds and piety are matchless. However, it has been set that the Holy Prophet (Allah bless him and grant him peace) would, in his supplications, frequently say statements meaning: “O Allah! We have not fulfilled the right of Your worship, as its right is. We have not recognized You as Your right is. We have not  acquired the piety as Your right deserves. We ask forgiveness for our shortcomings in fulfilling Your rights.”
 
In another Hadith, it is mentioned, “O people! Repent to Allah and seek his forgiveness. Verily, I repent 100 times in a day” (Muslim).

In the previously mentioned Hadith, the count was not specified, but in this Hadith, it is specified to be 100. Therefore, when our elders instruct people on adkhar, tasbihaat, and ma’mulaat, they always include 100 times istighfar (seeking forgiveness) with the following words:  

استغفر الله ربي من كل ذنب وأتوب إليه

The word tawba (seeking repentance) is also included here; however, it is also important that we also make the intention for seeking repentance.

So if the Holy Prophet (Allah bless him and grant him peace) used to seek Allah’s forgiveness 100 times in a day, and this is also included in the routine of our elders, then we should also bring this deed into practice.”

Tawba ki Haqeeqat Aur Ahmiyat

(Translated by brother I Khan)