On Purim, during the repetition of the Shemone Esray for Shacharis, there is a custom by some to add Krovitz, which discusses events from Purim. The Krovitz is added before reciting the actual bracha in each blessing of Shemone Esray except for Es Tzemach Dovid. The reason for this is because Es Tzemach Dovid talks of the rise of Moshiach which comes from the tribe of Yehuda and the events of Purim was through Mordechai and Esther, who were from the tribe of Binyomin (which was the tribe Shaul HaMelech came from).