Taanis, Chapter Two, Mishnah 7. In the previous Mishnah we dealt with the status of the kohanim of the mishmar (watch) serving in the Beis HaMikdash during the week in which the fasts fall, and with the status of the men of the beis av - the kohanim serving on one particular day of that week. Our Mishnah continues with the same subject, and discusses the laws that apply to them throughout the entire year.
The law of drinking wine:
"Anshei mishmar mutarim lishtos yayin ba'leilos aval lo ba'yamim" - the kohanim of that week's watch may drink wine at night, for although they may be needed to assist in the service of the Beis HaMikdash when the workload is too great for the men of the beis av, this happens only during the day and not at night. During the day, however, they are forbidden to drink wine, since one who has drunk wine may not perform the service in the Beis HaMikdash.
"V'anshei beis av lo ba'yom v'lo ba'lailah" - the kohanim of the beis av, who serve on that particular day, are forbidden to drink wine during the day, when they are engaged in the service, and also at night, because service may be required at night as well - especially since many kohanim would be bringing up the fats and the limbs of the day's offerings all through the night.
The prohibition of haircutting and laundering:
"Anshei mishmar v'anshei ma'amad asurin mi'lesaper u'mi'lechabes" - this prohibition applies both to the kohanim of the weekly watch and to the men of the ma'amad: those Israelites who represent all of Israel at that time and who are present when the offerings are brought. The reason: so that they should not put these tasks off until the time when they need to be occupied with the offerings, but rather attend to them in advance, entering that week already having had their hair cut and with their clothing laundered.
"U'va'chamishi mutarin" - on Thursday they were permitted to cut their hair and launder their clothing, in honor of Shabbos.
In summary: in this Mishnah we learned the laws that apply to the men of the mishmar, the men of the beis av and the men of the ma'amad throughout the year: the men of the mishmar are permitted wine at night and forbidden it during the day, the men of the beis av are forbidden it both by day and by night, and the men of the mishmar and the men of the ma'amad are forbidden to cut their hair and launder their clothing all that week - and on Thursday they were permitted to do so, in honor of Shabbos.