"But You promised." This is the hinge of Jacob's prayer in Targum Pseudo-Jonathan (Genesis 32:13). After naming his fears, after invoking his fathers, after shrinking himself into honest smallness, Jacob plays his last card: the word of God.
"You promised, I will surely do you good, and I will make your sons as many as the sand of the sea, which cannot be numbered for multitude." Notice the logic. If Esau kills the mothers with the children tonight, the promise God Himself made becomes impossible. The sand of the sea cannot come from a man whose children were slaughtered at the Jabbok.
Holding the Holy One to His word
The rabbis treasured this kind of boldness. Abraham bargains over Sodom; Moses tells God to blot him out of the book; Jacob here reminds God that His own oath is on the line. In each case the patriarch is not defying God — he is taking God seriously enough to cite Him back to Himself. It is the highest kind of faith: the faith that assumes the Holy One keeps His word.
The takeaway: Jewish prayer is a conversation, not a monologue. Jacob reads God's promise back to Him, and then he sleeps.