הלכה על קידושין 137:18

From the laws of the commandment is that which they, may their memory be blessed, said (Yevamot 49a and see Mishneh Torah, Forbidden Intercourse 15:1) that the mamzer that the Torah forbade is one that is born from the sexual prohibitions mentioned in the Torah, except from a menstruant women - as a son from her is defective, but he is not called a mamzer. And whether it was under coercion or volitional, in any case, he is called a mamzer. And [if] a gentile or a slave has sexual relations with a daughter of Israel, the offspring is fitting (as opposed to being a mamzer) - whether she is single or whether she is the wife of a man, whether it is under coercion or whether it is volitional. But [if] a gentile or a slave has sexual relations with a mamzeret, the offspring is a mamzer, but if a mamzer has sexual relations with a gentile woman, the offspring is a gentile - and if he converts, he is fitting immediately, like all of the converts of the nations (Yevamot 45b and see Mishneh Torah, Forbidden Intercourse 15:3-4). And if he has sexual relations with a slave woman, the offspring is a slave. And if [his master] freed him, the offspring is fitting, like other freed slaves - and they are permitted to come (marry) into the congregation of Israel. This is the general principle: A son that comes from a slave woman or a gentile woman or from a slave or from a gentile or from a mamzer, the offspring is like [the woman] and we do not pay attention to the [identity of the] father at all. And because of this thing, the Sages permitted (Kiddushin 69a) a mamzer to marry a slave woman, in order to 'purify' his children - as behold, he frees them and they are found to be free men. And a mamzer is permitted to marry a woman convert and a woman mamzer is permitted to marry a convert, as it states, "into the congregation of the Lord" - and the congregation of converts is not called a congregation - and [in these cases,] the offspring follows the defective one (see Mishneh Torah, Forbidden Intercourse 15:7,9). And even [if] a convert marries [another] convert, [their] son is permitted to [marry] a mamzeret, from the reason that we mentioned - even though his conception and his birth were in purity (after they converted). And [this is the case] even [for] his children and grandchildren until the name of gentileness is removed from them, meaning to say that it is not known that he is [descended from converts]. But [if] a convert marries a daughter of Israel or a son of Israel marries a convert, the offspring is an Israelite in all matters and forbidden to marry a mamzer woman. And the rest of the details of the commandment are elucidated in the eighth chapter of Yevamot and at the end of Kiddushin (see Tur, Even HaEzer 4).