Negative commandment · Lo Ta’aseh #205 of 613
[For a Nazarite] not to eat grape seeds
שלא יאכל חרצנים
The verse · Bamidbar 6:4
כֹּל יְמֵי נִזְרוֹ מִכֹּל אֲשֶׁר יֵעָשֶׂה מִגֶּפֶן הַיַּיִן מֵחַרְצַנִּים וְעַד־זָג לֹא יֹאכֵל
“All the days of his abstinence shall he eat nothing that is made of the vine tree, from the kernels even to the husk.”
The Rambam’s words
[For a Nazarite] not to eat grape seeds, as [Numbers 6:4] states: "He shall not eat [anything from wine grapes] from its seeds...."
שלא יאכל חרצנים, שנאמר "מחרצנים . . . לא יאכל" (במדבר ו,ד).
Where in the Mishneh Torah
Hilchot Nazariteship הלכות נזירות