Ketubot

[Now] does it not  mean that if he had [yet] no intercourse [with his wife] he may have intercourse [with her] even on Sabbath?2   — Said Raba: No, except Sabbath. Said Abaye to him: But it says, 'until the night following the Sabbath [one gives her] four nights'?3   — Only, said Raba, when he already had intercourse [with her].  If [it were, as you say,] after he already had intercourse, what does he let us hear?  — He lets us hear that it is allowed to have intercourse on Sabbath, as that [statement] of Samuel [teaches], for Samuel said: One may enter into a narrow opening on Sabbath,  although  he causes pebbles to break loose.