leviticus 5:6 And he shall bring his trespass offering unto the LORD for his sin which he hath sinned, a female from the flock, a lamb or a kid of the goats, for a sin offering; and the priest shall make an atonement for him concerning his sin. - Free Bible Online

      6-14. he shall bring his trespass offering unto the Lord for his sins which he hath sinned--A trespass offering differed from a sin offering in the following respects: that it was appointed for persons who had either done evil unwittingly, or were in doubt as to their own criminality; or felt themselves in such a special situation as required sacrifices of that kind [BROWN]. The trespass offering appointed in such cases was a female lamb or kid; if unable to make such an offering, he might bring a pair of turtledoves or two young pigeons--the one to be offered for a sin offering, the other for a burnt offering; or if even that was beyond his ability, the law would be satisfied with the tenth part of an ephah of fine flour without oil or frankincense.

JFB.