daf bit: Moed Katan 17

The mishna lists those who are allowed to cut their hair during the intermediate days of festivals (all others are forbidden): one arriving home from abroad or from a place of captivity, one coming out of prison, one who was under a ban and the sages have just granted absolution, and a nazarite or metzora (leper) on emerging to begin his purification. The g'mara on today's daf discusses this last part: is this concession (to cut one's hair) only at the first opportunity, or can one who had an earlier opportunity but did not take it cut his hair later? R. Zera quotes a baraita saying that all those listed in the mishna are permitted only if they did not have an earlier opportunity, but for the nazarite and the leper, they are permitted regardless. Why? Because they should not delay bringing their (prescribed) offerings on their release from their restrictions, and (apparently?) they can't bring those offerings until after they cut their hair. (mishna 13b, g'mara 17b)

A baraita, for those who are wondering, is a teaching contemporary with the mishna that was not recorded in the mishna. So, older than g'mara, but oral transmission for longer.