It wasnarrated from Abu Hurairah that the Messenger of Allah (ﷺ)said:
"The martyr does not feel anything more when he is killed thanoneof you feels if he is pinched (by a bug)." (ID)
English reference (ID): Vol. 4, Book 24, Hadith 2802 (ID)
Arabic reference (ID): Book 24, Hadith 2908 (ID)