Genesis 4:1 (BSB)

And Adam had relations with his wife Eve, and she conceived and gave birth to Cain. “With the help of the LORD I have brought forth a man,” she said.

From Genesis 4. Also in the ESV.

Commentary on Genesis 4:1

• John Calvin (Reformed), Calvin's Commentaries on Genesis 4:1: 1. And Adam knew his wife Eve . Moses now begins to describe the propagation of mankind; in which history it is important to notice that this benediction of God, “Increase and multiply,” was not abolished by sin; and not only so, but that the heart of Adam was divinely confirmed so that he did not shrink with horror from the production of offspring.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Genesis 4:1-2: Adam and Eve had many sons and daughters, Gen 5:4. But Cain and Abel seem to have been the two eldest. Some think they were twins, and, as Esau and Jacob, the elder hated and the younger loved. Though God had cast our first parents out of paradise, he did not write them childless; but, to show that he had other blessings in store for...
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Genesis 4:1: And Adam knew Eve his wife,.... An euphemism, or modest expression of the act of coition. Jarchi interprets it, "had known", even before he sinned, and was drove out of the garden; and so other Jewish writers, who think he otherwise would not have observed the command, "be fruitful and multiply": but if Adam had begotten children in a state of innocence, they would have...
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on Genesis 4:1: And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD. (a) Man's nature, the estate of marriage, and God's blessing were not utterly abolished through sin, but the quality or condition of it was changed.