Rowan Williams provides a translation of Arius’ Thalia in his classic Arius: Heresy and Tradition, in which Arius said:
For him it is impossible to search out the mysteries of the Father, who exists in himself (eph’ heautou); For the Son does not [even] know his own substance, Since, being a son, he came into actual subsistence (hupērxen alethōs) by a father’s will (thelēsei potros). What scheme of thought (logos), then, could admit the idea that he who has his being from the [a?] Father (ton ek patros onta) Should know by comprehension (en katalepsei) the one who gave him birth? For clearly the one who has a beginning (to archēn echon) is in no way [in a position] to encompass in thought or lay hold upon the one without beginning as he is [in himself] (hōs estin).
Arius: Heresy and Tradition, 103.
Apparently, Arius must have been unfamiliar with Matthew’s Gospel. Jesus is there quoted as saying, “All things have been handed over to me by my Father, and no one knows the Son except the Father, and no one knows the Father except the Son and anyone to whom the Son chooses to reveal him” (Matt 11:27).