question #1 Sahih Muslim 936a, Book 11, Hadith 41 : What is the significance of taking an oath of allegiance in Islam?

The Messenger of Allah (ﷺ) took a promise from us along with the oath of Allegiance that we would not lament. But only five among us fulfilled the promise (and they are) Umm Sulaim, and Umm al-‘Ala’, and the daughter of Abu Sabra the wife of Mu’adh, or daughter of Abu Sabra and wife of Mu’adh.