question #2 Sahih Muslim 715a, Book 6, Hadith 86 : How does the act of performing additional prayers relate to gratitude and fulfillment of obligations in Islamic teachings?

The Apostle of Allah (ﷺ) owed me a debt; he paid me back and made an addition (of this). I entered the mosque and he (the Holy Prophet) said to me: Observe two rak’ahs of prayer.