What’s the verse, IN TORAH ITSELF, that says we can’t let someone die

I’m starting to forget things**. What is the sentence, from Torah itself, that says we can’t let someone drown or maybe it’s die. if we can save him? What the chapter and verse if you know that too? **I keep learning new things and it seems to be forcing out some of the old things. I’ve been trying to recall this for 2 days and I want to tell someone about it.