Midrash su Levitico 20:9

1) (Vayikra 20:9) ("For a man, a man, who curses his father and his mother shall be put to death. He has cursed his father and his mother; his blood is in him.") "A man": This tells me only of a man. Whence do I derive (the same for) a woman? From "A man, a man." "who curses his father": and not the father of his father. "and his mother": and not the father of his mother. "his father": (one who is) definitely (his father), and not one (whose paternity is) in doubt. "his mother": definitely, and not in doubt.

2) "He has cursed his father and his mother": What is the intent of this? Because it is written (Shemoth 21:19) "And he who curses his father and his mother shall be put to death," I might think that he is not liable until he curses both of them; it is, therefore, written "He has cursed his father; ("He has cursed) his mother" — either one. A proselyte, then, is liable for (cursing) his mother, but not for (cursing) his father, (there being no "fatherhood" for a proselyte.) These are the words of R. Yossi Haglili. R. Akiva says: "He has cursed his father and his mother": One who is liable for (cursing) his father is liable for (cursing) his mother. One who is not liable for his father is not liable for his mother. R. Akiva concedes that a shtuki (an illegitimate child of unknown fatherhood) is liable for (cursing) his mother even though he is not liable for (cursing) his father.

3) Variantly: "He has cursed his father and his mother": even after death. For (without this verse) would it not follow (that he is not liable), viz.: The striker (of his parents) is liable, and the curser is liable. Just as the striker is liable only in their lifetime, so, the curser. It must, therefore, be written "He has cursed his father and his mother" — even after death. "His blood is in him": (He is to be put to death) by stoning.