Book of Mormon:
Therefore I say unto you, that he that will not hear my voice, the same shall ye not receive into my church, for him I will not receive at the last day. Therefore I say unto you, Go; and whosoever transgresseth against me, him shall ye judge according to the sins which he has committed; and if he confess his sins before thee and me, and repenteth in the sincerity of his heart, him shall ye forgive, and I will forgive him also. 30 Yea, and as often as my people repent will I forgive them their trespasses against me….Now I say unto you, Go; and whosoever will not repent of his sins the same shall not be numbered among my people; and this shall be observed from this time forward….
And it came to pass that Alma went and judged those that had been taken in iniquity, according to the word of the Lord. And whosoever repented of their sins and did confess them, them he did number among the people of the church; And those that would not confess their sins and repent of their iniquity, the same were not numbered among the people of the church, and their names were blotted out. (Mosiah 26:28-36)
Know ye not that a little leaven leaveneth the whole lump? Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us: Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth. I wrote unto you in an epistle not to company with fornicators: Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world. But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat. For what have I to do to judge them also that are without? do not ye judge them that are within? But them that are without God judgeth. Therefore put away from among yourselves that wicked person. (1 Corinthians 5:6-13)