Reference : Hisn al-Muslim 153

من كان آخر كلامه "لا إله إلا الله" دخل الجنة
Lā ilāha illallāh

Whoever dies with the last words (whose meaning is): "There is none worthy of worship but Allah" will enter Paradise.

Reference:
Abu Dawud 3/190. See also Al-Albani, Sahihul-Jami' As-Saghir 5/432.

Chapter: Instruction for the one nearing death