What he ﷺ said while dying
Aisha watched him dipping his hand in water and wiping his face.
لاَ إِلَهَ إِلاَّ اللَّهُ، إِنَّ لِلْمَوْتِ سَكَرَاتٍ
Lā ilāha illa-llāh, inna li-l-mawti sakarāt.
“There is no god but Allah. Indeed, death has its agonies.”
He did not describe it as gentle. The one person who could have been spared it was not, and said so.
The full narration
Narrated Aisha:It was one of the favors of Allah towards me that Allah's Messenger (ﷺ) expired in my house on the day of my turn while he was leaning against my chest and Allah made my saliva mix with his saliva at his death. `Abdur-Rahman entered upon me with a Siwak in his hand and I was supporting (the back of) Allah's Messenger (ﷺ) (against my chest ). I saw the Prophet (ﷺ) looking at it (i.e. Siwak) and I knew that he loved the Siwak, so I said ( to him ), "Shall I take it for you ? " He nodded in agreement. So I took it and it was too stiff for him to use, so I said, "Shall I soften it for you ?" He nodded his approval. So I softened it and he cleaned his teeth with it. In front of him there was a jug or a tin, (The sub-narrator, `Umar is in doubt as to which was right) containing water. He started dipping his hand in the water and rubbing his face with it, he said, "None has the right to be worshipped except Allah. Death has its agonies." He then lifted his hands (towards the sky) and started saying, "With the highest companion," till he expired and his hand dropped down
Source
Ṣaḥīḥ al-Bukhārī · 4449
- Agreed upon as authentic (al-Bukhārī / Muslim)