Related for Megillah 1:4
קָרְאוּ אֶת הַמְּגִלָּה בַּאֲדָר הָרִאשׁוֹן וְנִתְעַבְּרָה הַשָּׁנָה, קוֹרִין אוֹתָהּ בַּאֲדָר הַשֵּׁנִי, אֵין בֵּין אֲדָר הָרִאשׁוֹן לַאֲדָר הַשֵּׁנִי אֶלָּא קְרִיאַת הַמְּגִלָּה וּמַתָּנוֹת לָאֶבְיוֹנִים:
If they read the Megillah on the first Adar, and they intercalated the year, they read it on the second Adar. There is no difference between the first Adar and the second Adar but the reading of the Megillah and matanoth la'evyonim alone. [This is what is meant: There is no difference between the fourteenth and fifteenth of the first Adar and the fourteenth and fifteenth of the second Adar but the reading of the Megillah and matanoth la'evyonim, (which obtain on the second and not on the first). But in respect to eulogy and fasting, they are alike (i.e., they are forbidden on both.)]