Panarion 78.6.1 (the Antidikomarianites) — as quoted by Pitre (p 114); translation: as summarised by Pitre (endnote), from Frank Williams's translation
Epiphanius describes a heretical group in Arabia known as the 'Insulters of Mary' (Greek Antidikomarianites) and calls their rejection of Mary's perpetual virginity 'a novel madness.'
No freely usable English translation of this passage is online, so the note keeps Pitre's quotation and links to the full text. Translation: as summarised by Pitre (endnote), from Frank Williams's translation.
In Jewish Roots of Mary
Why it is cited
The 'Insulters of Mary' in Arabia denied her perpetual virginity; Epiphanius calls their view 'a novel madness' — evidence that the doctrine was the ancient consensus and its denial the innovation.