Are you talking about the parable in Luke 18?
In it, the widow constantly asks the judge for a just judgment. Jesus then explains the parable: “Will not God then secure the rights of his chosen ones who call out to him day and night?” In other words, just as the widow petitioned the judge, Jesus explains what happens when we petition God. That is, when we petition God ‘day and night.’ For the same thing – just as the widow did. Your logic doesn’t hold here, you know…
Let’s look at that context, then. In Luke 11, we see Jesus’s command:
εἶπεν δὲ αὐτοῖς ὅταν προσεύχησθε λέγετε· Πάτερ,
(And he said to them, “When you pray, say, ‘Father, …’”)
Note that the word ‘say’ (λέγετε) is an imperative: Jesus is telling them “Say (this)!”. He’s not telling them “Say (something like this)”, but rather, he’s giving them an order: “Say ‘Father, …’”.