Is a person considered among the transgressors in the sight of God and the Quran if he vows to God or swears that he will be so upon committing a specific sin, and then actually commits it?

Injustice varies; some types remove one from the fold of Islam, like disbelief (kufr), while others do not, like sins (ma'asi). The term "unjust person" (zalim) may refer to a disbeliever or a sinner. Accordingly, if testifying against oneself with injustice means falling into sin, then this is an acknowledgment of reality, and repentance and uprightness are obligatory. If it means polytheism (shirk), then this is a forbidden statement from which repentance and seeking forgiveness are obligatory. It is not considered an oath, nor does disbelief occur thereby, nor is expiation (kaffarah) required for it. However, if one intends to approve of it by doing so, then he is an immediate disbeliever.