(Devarim 16:10) "And you shall make a festival of weeks (shavuoth) to the L-rd your G-d": Because it is written (Shemoth 23:16) "And the festival of the harvest (Shavuoth) the (time of bringing the) first-fruits of your labor," I might think, if you "harvest, you make a festival, and if not, you do not make a festival; it is, therefore, written "and you shall make a festival of weeks to the L-rd your G-d" — Whether or not you have a harvest, you make a festival.
(דברים טז י) וְעָשִׂיתָ חַג שָׁבֻעוֹת לַה׳ אֱלֹהֶיךָ, מִכְּלָל שֶׁנֶּאֱמַר (שמות כג טז) ״וְחַג הַקָּצִיר בִּכּוּרֵי מַעֲשֶׂיךָ״ יָכוֹל אִם יֵשׁ לְךָ קָצִיר אַתָּה עוֹשֶׂה יוֹם טוֹב, וְאִם לָאו אִי אַתָּה עוֹשֶׂה יוֹם טוֹב? תַּלְמוּד לוֹמַר: וְעָשִׂיתָ חַג שָׁבֻעוֹת לַה׳ אֱלֹהֶיךָ, בֵּין שֶׁיֵּשׁ לְךָ קָצִיר וּבֵין שֶׁאֵין לְךָ קָצִיר אַתָּה עוֹשֶׂה יוֹם טוֹב.
(Devarim 16:10) "And you shall make a festival of weeks (shavuoth) to the L-rd your G-d": Because it is written (Shemoth 23:16) "And the festival of the harvest (Shavuoth) the (time of bringing the) first-fruits of your labor," I might think, if you "harvest, you make a festival, and if not, you do not make a festival; it is, therefore, written "and you shall make a festival of weeks to the L-rd your G-d" — Whether or not you have a harvest, you make a festival.
מִסַּת נִדְבַת יָדְךָ אֲשֶׁר תִּתֵּן, מְלַמֵּד שֶׁאָדָם מֵבִיא חוֹבָתוֹ מִן הַחֻלִּין.
"the tribute of the offering of your hand": We are hereby taught that one brings his obligatory offering from chullin (non-consecrated monies).
מִנַּיִן שֶׁאִם רָצָה לְהָבִיא מִמַּעֲשֵׂר יָבִיא? תַּלְמוּד לוֹמַר: כַּאֲשֶׁר יְבָרֶכְךָ ה׳ אֱלֹהֶיךָ.
And whence is it derived that if he wishes, he may include some of his tithe monies? From "as the L-rd your G-d will bless you."