Perhaps you are referring to Sotah 37a? (I would copy and paste the original source text but unfortunately Hebrew characters posted on Lookjed do no display properly on my computer.) The Talmud there states:
"R. Judah said to [R. Meir]: That is not what happened; but each tribe was unwilling to be the first to enter the sea. Then sprang forward Nahshon the son of Amminadab and descended first into the sea; as it is said: Ephraim compasseth me about with falsehood, and the house of Israel with deceit; but Judah yet ruleth with God. Concerning him it is stated in Scripture, Save me O God, for the waters are come in unto my soul. I sink in deep mire, where there is no standing etc. Let not the waterflood overwhelm me, neither let the deep swallow me up etc."
From the Soncino: [
halakhah.com]
Tzvi Daum
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