Rashi on Exodus 21:15/רש"י על שמות כ״א:ט״ו

1ומכה אביו ואמו AND HE THAT SMITETH HIS FATHER OR HIS MOTHER [SHALL SURELY BE PUT TO DEATH] — Because Scripture has taught us that he who inflicts a wound upon his fellow-man is liable for damages (cf. Rashi on Exodus 21:24) but is not subject to death, it was compelled to state that he who inflicts a wound on his father or his mother is subject to the death penalty (Mekhilta). He is, however, not punishable with death except for a blow which causes a wound (Sanhedrin 85b).

2אביו ואמו means either his father or his mother (Mekhilta).

3מות יומת SHALL BE PUT TO DEATH — by strangulation (Mekhilta).