Kitāb-ut-Tawheed : Chapter 2:
The Excellence of Tawheed and the Sins it wipes away
‘Itban (radi Allaahu anhu) narrated that the Prophet (sallAllaahu `alayhi wa sallam) said:
“Indeed Allah has forbidden for Hell the person who testifies: ‘There is nothing worthy of worship in truth (no true God) but Allah’, seeking thereby nothing but Allah’s Face (pleasure).”
(Al-Bukhari, Muslim).