Sunan Ibn Majah
297
Sahih+2

It was narrated that 'Ali said:"The Messenger of Allah said: 'The screen between the Jinn and the nakedness of the sons of Adam is that when a person enters the Kanif, he should say: Bismillah (in the name of Allah)

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi