The word(s) "mistake" appears 4 time(s) in 3 verse(s) in Quran in Muhammad Pickthal translation.

(1) It is not for a believer to kill a believer unless (it be) by mistake. He who hath killed a believer by mistake must set free a believing slave, and pay the blood-money to the family of the slain, unless they remit it as a charity. If he (the victim) be of a people hostile unto you, and he is a believer, then (the penance is) to set free a believing slave. And if he cometh of a folk between whom and you there is a covenant, then the blood-money must be paid unto his folk and (also) a believing slave must be set free. And whoso hath not the wherewithal must fast two consecutive months. A penance from Allah. Allah is Knower, Wise.

(2) Of mankind is he who saith: We believe in Allah, but, if he be made to suffer for the sake of Allah, he mistaketh the persecution of mankind for Allah's punishment; and then, if victory cometh from thy Lord, will say: Lo! we were with you (all the while). Is not Allah Best Aware of what is in the bosoms of (His) creatures?

(3) Proclaim their real parentage. That will be more equitable in the sight of Allah. And if ye know not their fathers, then (they are) your brethren in the faith, and your clients. And there is no sin for you in the mistakes that ye make unintentionally, but what your hearts purpose (that will be a sin for you). Allah is ever Forgiving, Merciful.