Irenaeus — Against Heresies 5.21.1
Summing up all things, then, he also summed up the war against our enemy, crushing the one who at the beginning in Adam had led us captive, and treading his head — as you have in Genesis God saying to the serpent: “I will put enmity between you and the woman, and between your seed and her seed; he will watch your head, and you will watch his heel.”
For from him who was to be born of a virgin woman according to Adam’s likeness, it was proclaimed that he watches the serpent’s head — that is, the seed of which the Apostle speaks.
Latin
Omnia ergo recapitulans recapitulatus est, et adversus inimicum nostrum bellum provocans, et elidens eum qui in initio in Adam captivos duxerat nos, et calcans eius caput, quemadmodum habes in Genesi dixisse serpenti Deum: Et inimicitiam ponam inter te et inter mulierem, et inter semen tuum et semen eius: ipse tuum observabit caput, et tu observabis eius calcaneum. Ex eo enim qui ex muliere Virgine habebat nasci secundum similitudinem Adam, praeconabatur observans caput serpentis, id est semen, de quo ait Apostolus…