question #1 Sahih Muslim 243, Book 2, Hadith 43 : What is the significance of performing ablution thoroughly in Islamic practice?

‘Umar b. Khattab said that a person performed ablution and left a small part equal to the space of a nail (unwashed). The Apostle of Allah (ﷺ) saw that and said: Go back and perform ablution well. He then went back (performed ablution well) and offered the prayer.