Halakhah zu Tehillim 139:21

And this entire issur of lashon hara applies only [when spoken] against the man who is in the category of "your neighbor" [amitecha], "am she'techa," "a people who is with you" in Torah and in mitzvoth. But those people whom he knows to have "apikorsoth" [heresy] among them, it is a mitzvah to demean and to shame, both in their presence and not in their presence, in everything that he sees or hears about them. For it is written (Vayikra 25:17): "And you shall not wrong, one man, his fellow [amito]" and (Vayikra 19:16): "You shall not go talebearing among your people [be'amecha]." And they are not in this category, for they do not act as Your people. And it is written (Tehillim 139:21): "Do I not hate your haters, O L–rd? And against those who rise up against You do I strive." And one who denies the Torah and prophecy of Israel, both the written and the oral Law, is called an apikoress [heretic], even if he says all the Torah is from Heaven, except for one verse, or one kal vachomer [a fortiori argument], or one gezeirah shavah [identity deduction], or one dikduk [inference].

And it is practiced in every place and at all times by males and females. And one who transgresses it and fixes hatred in his heart towards any proper Israelite has violated this negative commandment. But we do not administer lashes for it, as there is no act [involved] with it. But there is no prohibition in the hatred of the evildoers, but rather [it is] a commandment to hate them, after we rebuke them about their sin many times and they do not want to return, as it is stated (Psalms 139:21), "Do I not, Lord, hate Your enemies, and argue with those that come against You."

And so [too,] did they, may their memory be blessed, say (Mishneh Torah, Laws of Mourning 1:10) [regarding] those that separate themselves from all the ways of the community, and likewise heretics, apostates and informants - that we do not mourn at all for all of them, since their death is gladness for the world. And this is not a punishment for their relatives, but rather a merit for them. And this is all from the root that I wrote. And about them is stated (Psalms 139:21), "Do I not hate those You hate?" And likewise, we do not mourn for one who kills himself on purpose. And in its place, it is clarified how we know that he struck himself on purpose. And also from the laws of the commandment are the things that they, may their memory be blessed, said (Moed Katan 21a) that the mourner is forbidden with on the first day from Torah writ and the rest of the days rabbinically; the law of seven and thirty [days]; the law of twelve months of mourning for father and mother; the law of tearing - who are the relatives who tear and what is the time [for it], how is it for [other] relatives and how is it for father and mother, for which of his relatives, and his teacher and his greats, for which places in the Land of Israel in their destruction; the law of the tear that we darn immediately or after a time and the law that a woman darns immediately so as not be disgraced; the law of the holidays that interrupt [the count] and do not count [in the tally], and that which they said (Moed Katan 19a) that the decree of seven is negated for anyone who buries his dead even an hour before the holiday, and the decree of thirty is negated if seven days passed before the holiday and he began even one hour of the thirty [days], and that the status of Rosh Hashanah and Yom Kippur is the same as the holidays of Pesach, Shevouot and Sukkot; that which they said (Moed Katan 24b) that even though there is no mourning on the intermediate days of the festival, a man tears for a dead [relative] for which he is obligated to mourn; the law that we only observe one day and do not tear for a distant report [of death] after thirty days, - since the law is like Rabbi Mani, who said like this in the Gemara [Moed Katan 21b] - but he tears even for a distant report for his father and for his mother according to the opinion of Ramban, may this memory be blessed, (Torat HaAdam 61b), but not according to the opinion of the rabbi, Rabbi Avraham beRebbi David (Ravad), may his memory be blessed.