All of your works shall praise You, Hashem our G-d, and your pious ones, the righteous ones who do Your will; and all of Your people, the House of Israel will thank and bless in joyful song, and extol and glorify, and exalt and acclaim, and sanctify and coronate Your name, our King. Since, You it is good to thank, and to Your name it is pleasant to sing, since from always and forever are you G-d.
)
Are there sources for drinking a fifth cup at the Seder?