Jesus talks about his father a lot. Is it Yahweh? How do we know that when Jesus says, "My father" he means Yahweh from the Old Testament?
Multiple ways, though not all of them are obvious in the English translation.
Jesus refers to himself with 'I AM' in a manner as to make a direct connection to Yahweh from the Old Testament.
EDIT Somebody wanted more specificity, so if you read the whole passage Jesus says clearly to the Jews...
Doesn't get much clearer than that. The God of the Jews is Yaweh. Jesus says that the God they claim is his Father.