- Peninei Halakha
One may wash one’s hands for the sake of a mitzva because such washing is not for the purpose of gaining pleasure. Therefore, Kohanim may wash their hands in preparation for Birkat Kohanim (Rema 613:3, sa 128:6). However, one may not immerse in a mikveh on Tisha Be-Av.7
Upon awakening in the morning, each person must wash his hands from the tips of the fingers to their base, because an evil spirit rests on one’s hands after a night’s sleep, and it can harm the orifices of one’s body. In order to remove this spirit, one must wash each hand three times alternately. After using the bathroom, one should wash his hands again once and recite the berakha of "al netilat yadayim," because the Sages instituted a mitzva to wash one’s hands with a berakha in preparation for Shaĥarit. Even though we usually take care to wash the entire hand, on Tisha Be-Av one should wash only up to the base of one’s fingers, including the knuckles, because technically that is sufficient both for preparing for Shaĥarit and for removing the evil spirit (sa 613:2).8
Le-khatĥila, one should wash his hands before every prayer service throughout the year. Nevertheless, on Tisha Be-Av one should not wash his hands before praying, because doing so is not obligatory. However, if one touched filthy parts of his body and wants to recite sacred words, he should wash his hands, because this washing is for the sake of a mitzva, not in order to derive pleasure (mb 613:5-6, Kaf Ha-ĥayim 613:6).
There is uncertainty regarding the status of one who relieves himself without touching any part of the body that is usually covered, as perhaps he does not need to wash, since he did not touch any filth. In order to avoid this uncertainty, when one relieves oneself on Tisha Be-Av it is best to touch a part of the body that is usually covered and sweaty. This way, all agree that one may wash his hands until the base of one’s fingers, including the knuckles, in order to recite the berakha of Asher Yatzar in a state of cleanliness (sa 613:3, mb ad loc. 4).9
7The mitzva for a nida (a woman who has menstruated and who must immerse in a mikveh before resuming relations with her husband) to immerse herself in a mikveh at the first halakhically acceptable opportunity does not override the prohibition against washing on Tisha Be-Av. Similarly, a man who usually immerses in a mikveh in order to remove the impurity caused by a seminal emission may not immerse on Tisha Be-Av, because a pious custom does not override the prohibition against washing (Beit Yosef, 554:8, 613:11).
8According to most poskim, one does not need to wash one’s hands more than once after using the bathroom; but some people are accustomed to washing three times (see 4:39). Those who always wash three times may do so on Tisha Be-Av as well, because this washing is for the sake of purification and a mitzva, not pleasure (see Peninei Halakha: Prayer 8:3-5 and n. 2).
9Some say that one who touches a part of the body that is usually covered should wash only that hand until the base of one’s fingers (Ĥayei Adam 40:18, 613:6). Others maintain that he must wash both hands (Shlah, Yafeh La-lev; see also Kaf Ha-ĥayim 4:86). They also disagree about a case in which one touches his shoe – even if it is made of cloth – with one finger. There are many other uncertainties regarding these laws. For example, does one who touches an area that is usually covered, but which nonetheless is not sweaty, need to wash his hands (see Peninei Halakha: Prayer, ch. 5 n. 2)? Furthermore, technically, one who touches body parts that are usually covered may simply rub his hands on any sort of cloth and then recite sacred words ( 4:23, ad loc. 61). Why, then, do we not do so on Yom Kippur and Tisha Be-Av? In practice, it appears that if, in a certain situation, one generally is stringent throughout the year and washes his hands, he should wash them on Tisha Be-Av as well, because he is washing for the sake of a mitzva. If, however, he sometimes suffices with rubbing his hands on his clothing or the like, he should do the same on Tisha Be-Av. If one touches an area of his body that is usually covered and now wants to pray, he should wash his hands, because that is the halakha, as explained in Peninei Halakha: Prayer 5:2. If one touches an area of the body that is usually covered with one finger while in the bathroom, it seems that all would agree that he should wash both hands. After all, many authorities maintain that one must wash both hands upon leaving the bathroom, even if he did not relieve himself or touch a body part that is normally covered (see bhl 613:3). One who touches mud with his finger should wash only the soiled area, because there is no evil spirit there that spreads to the rest of the hand.