The disciples might say, If they have heard words from Thee, such as none other hath spoken, if they have seen works of Him, such as none other hath done, and yet have not been convinced, but have hated Thy Father, and Thee with Him, why dost Thou send us to preach? How shall we be believed? Such thoughts as these He now answers: But when the Comforter is come, Whom I will send unto you from the Father, even the Spirit of Truth which proceedeth from the Father, he shall testify of Me.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Hom. lxxvii. 2