וְעָשִׂ֜יתָ חַ֤ג שָׁבֻעוֹת֙ לַיהוָ֣ה אֱלֹהֶ֔יךָ מִסַּ֛ת נִדְבַ֥ת יָדְךָ֖ אֲשֶׁ֣ר תִּתֵּ֑ן כַּאֲשֶׁ֥ר יְבָרֶכְךָ֖ יְהוָ֥ה אֱלֹהֶֽיךָ׃
And thou shalt keep the feast of weeks unto the LORD thy God after the measure of the freewill-offering of thy hand, which thou shalt give, according as the LORD thy God blesseth thee.
Read halakhic rulings (Jewish law) on Deuteronomy 16:10: and classical halakhic sources.