XLVII. To the Faithful.
I admonish the faithful not to hold their brethren in hatred. Hatreds are accounted impious by martyrs for the flame. The martyr is destroyed whose confession is of such kind; nor is it taught that the evil is expiated by the shedding of blood. A law is given to the unjust man that he may restrain himself. Thence he ought to be free from craft; so also ought you. Twice do you sin against God, if you extend strifes to your brother; whence you shall not avoid sin following your former courses. You have once been washed: shall you be able to be immersed again?
Source: Writings (New Advent)