Augustine of Hippo
Catena Aurea · Johannesevangelium 8
Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it. And because I tell you the truth, ye believe me not. Which of you convinceth me of sin? And if I say the truth, why do ye not believe me? He that is of God heareth God’s words: ye therefore hear them not, because ye are not of God. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
(de Quæst. Nov. et Vet. Test. 2, 90) Or thus: The devil is not a singular, but a common name. In whomsoever the works of the devil are found, he is to be called the devil. It is the name of a work, not of a nature. Here then our Lord means by the father of the Jews, Cain; whom they wished to imitate, by killing the Saviour: for he it was who set the first example of murdering a brother. That he spoke a lie of his own, means that no one sins but by his own will. And inasmuch as Cain imitated the devil, and followed his works, the devil is said to be his father.