Reference : Hisn al-Muslim 151

جعل النبي صلى الله عليه وسلم عند موته يدخل يديه في الماء فيمسح بهما وجههُ ويقول :
لا إله إلا الله إن للموت لسكرات
As he was dying, the Prophet (ﷺ) dipped his hands in water and wiped his face saying:

Lā ilāha illallāh
inna li ‘lmawti la’sakarāt.

There is none worthy of worship but Allah, 
surely death has agonies.

Reference:
Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 8/144. The Hadith also mention him 
using the Siivak (tooth stick).

Chapter: When the sick have renounced all hope of life