Negative commandment · Lo Ta’aseh #354 of 613
For a mamzer not to marry a natural born Jewess
שלא יישא ממזר בת ישראל
The verse · Devarim 23:3
לֹא־יָבֹא מַמְזֵר בִּקְהַל ה׳ גַּם דּוֹר עֲשִׂירִי לֹא־יָבֹא לוֹ בִּקְהַל ה׳
“A bastard shall not enter into the congregation of the Lord; even to his tenth generation shall he not enter into the congregation of the Lord.”
The Rambam’s words
For a mamzer not to marry a natural born Jewess, as [Deuteronomy 23:3 states: "A mamzer may not enter G-d's congregation."
שלא יישא ממזר בת ישראל, שנאמר "לא יבוא ממזר, בקהל ה'" (דברים כג,ג).
Who & when
“And this prohibition is practiced in every place and at all times, by males and females.”
Where in the Mishneh Torah
Hilchot Forbidden Intercourse הלכות איסורי ביאה