For Rosh Chodesh or Pesach: haysa Yehudah lekadsho
pointing to the kiddush Hashem of the head of shevet Yehudah, Nacshon ben Aminadav, in jumping into the Yam Suf before it split. Rav Yaakov asks why the feminine form of the verb to be is used in "haysa"and answers that the verb references Tamar whose mesiras nefesh was behind the heroism of the day. She was willing to be killed rather than publicly shame Yehudah by naming him as the father of her unborn twins. As the matriarch of the tribe of Yehudah, she imbued this remarkable ability into her offspring. Thus Nachson acted as his great-great-great [I didn't count up actual number of generations] grandmother did in risking his life by plunging into the water.
It's a nice vort which got me to think of another possible interpretation of the use of the feminine verb in this instance, going back yet another generation (or 2, depending on how you look at it). I thought of Leah's naming Yehudah with the reason "hapa'am odeh es Hashem"-- this time I will give thanks to Hashem. Generations later, Yehudah's tribal head brought this idea to fruition for all of klal Yisrael. Krias Yam Suf gave rise to shirah, in which all the Jews gave thanks to Hashem for their salvation in words of song. Yehudahs embodied hoda'ah, which found its expression in Shiras Hayam.