It is narrated by Sayyidunā Farwaĥ bin Nawfal that once he presented himself in the blessed court of the
Noble and Beloved Prophet َ sallallahu alaihi wasallamِ,and asked اٰYā Rasūlallāĥ sallallahu alaihi wasallam
ّ  Tell me something that I can recite when getting into bed.’ The Beloved and Blessed
 Prophet sallallahu alaihi wasallamreplied, ‘Recite this sute kafirun
is relief from Shirk (Polytheism).’ (Sunan-ut-Tirmiżī, pp. 257, vol. 5, Ḥadīš 3414)