This episode from Christ's life is recounted in Saint John's Gospel; it was used by the scribes and Pharisees as a test of his orthodoxy.
According to Mosaic law, adulterous women were punished by stoning, and the woman's accusers wanted to find out if Christ would conform with the law; if he would not, they could then accuse him of breaking it.
Christ's response was to tell them, 'Let him who is without sin among you be the first to throw a stone at her'. The accusers dispersed without condemning her, and on being left alone with her, Christ told her that he would not condemn her either and commanded her not to sin again (John 8: 3-11).