Shama-il Tirmidhi Chapter 53, Hadith Number 3 (370).

Qaasim bin Muhammad Radiyallahu ‘Anhu reports that ‘Aayeshah Radiyallahu ‘Anha said: “I had seen Rasulullah Sallallahu ‘Alayhi Wasallam at the time of his death, a cup of water was near him. He was putting his hands in the cup and wiping his face with it. (At the time of intense heat and unrest it calms one). Then he was reciting: ‘O Allah help me in the difficulties of death'”.

Commentary
On one side it was a lesson to the ummah, and on the other side at the time of death, when the soul was leaving the body, it was a scene of complete steadfastness, perseverance and a total inclination towards Allah. At the time of death, when the soul was separated from the body, it is natural that pain was experienced. At that moment only Allah could be beseeched to make it easy.