The Father is true, and Jesus speaks what he has heard from the Father.

John 8:26, 28, 38, 40

²⁶I have many things to say and to judge of you: but he that sent me is true; and I speak to the world those things which I have heard of him.

²⁸Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am he, and that I do nothing of myself; but as my Father hath taught me, I speak these things.

³⁸I speak that which I have seen with my Father: and ye do that which ye have seen with your father.

⁴⁰But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham.