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

(1) It is not for a believer to kill a believer except (that it be) by mistake; and whosoever kills a believer by mistake, (it is ordained that) he must set free a believing slave and a compensation (blood-money, i.e. Diya) be given to the deceased's family unless they remit it. If the deceased belonged to a people at war with you and he was a believer, the freeing of a believing slave (is prescribed); and if he belonged to a people with whom you have a treaty of mutual alliance, compensation (blood-money - Diya) must be paid to his family, and a believing slave must be freed. And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months in order to seek repentance from Allah. And Allah is Ever All-Knowing, All-Wise.

(2) And do not kill anyone whose killing Allah has forbidden, except for a just cause. And whoever is killed wrongfully (Mazluman intentionally with hostility and oppression and not by mistake), We have given his heir the authority [to demand Qisas, - Law of Equality in punishment - or to forgive, or to take Diyah (blood money)]. But let him not exceed limits in the matter of taking life (i.e he should not kill except the killer). Verily, he is helped (by the Islamic law).

(3) Call them (adopted sons) by (the names of) their fathers: that is more just with Allah. But if you know not their father's (names, call them) your brothers in faith and Mawalikum (your freed slaves). And there is no sin on you concerning that in which you made a mistake , except in regard to what your hearts deliberately intend. And Allah is Ever Oft-Forgiving, Most Merciful.