Background
On most weekdays, after the chazzan’s repetition of the Amidah at both Shacharis and Minchah, a prayer of intense supplication is recited; this part of davening is referred to as Tachanun, lit., supplications. There are varying customs as to what text should be recited as part of Tachanun. Many communities begin the recitation of Tachanun with Vidui and the Thirteen Attributes of Mercy.107 Some have the custom to say the introductory verse Vayomer David before continuing with Racham VeChanun;108 the Vilna Gaon and other Poskim109 recommend against reciting this verse as it references Heavenly retribution.110 For the main body of Tachanun, Ashkenazim recite Chapter 6 of Tehillim (with the introductory verse of Rachum VeChanun), while Sephardim recite Chapter 25 (LeDavid, Eilecha). On Monday and Thursday, some recite the passages beginning Vehu Rachum before the section of Rachum Vechanun. Others follow the Arizal and recite Vehu Rachum after Rachum Vechanun.111 After Nefilas Apayim, additional supplications are recited while seated, and after the words of Va’anachnu lo neida, it is customary to rise.112
Now, in earlier times, the recitation of Tachanun involved actual prostration on the floor, albeit without spreading out one’s arms and legs. This practice is referred to as Nefilas Apayim. However, because there are many restrictions on prostration, we no longer prostrate ourselves to recite Tachanun. Nevertheless, as a commemoration of this practice and the restrictions that it entailed, the general custom is to lean one’s head to the side and cover one’s face while reciting Tachanun.113 This is done by resting one’s face upon his arm.114 However, because one cannot cover himself by using his own body, the custom is to place a separation, such as a tallis, or a suit or shirt sleeve, between one’s head and arm.115 Shulchan Aruch mentions conflicting customs as to which arm one should lean on,116 and the general custom is to lean on one’s right arm at Shacharis when tefillin are worn on the left arm, and to lean on the left arm at Minchah or when not wearing tefillin.117 A left-handed person always leans on his left arm.118
In many Sephardic communities, Tachanun is recited without any form of Nefilas Apayim.119 The universal custom is that women do not recite Tachanun.120
107 Sha’arei Teshuvah 131:1; Kaf Hachaim 131:10. Mishnah Berurah 134, note 1, indicates that there is a custom to recite these passages only on Monday and Thursday.
108 This verse is not included in any of the early editions of the siddur. It is, however, found in the Kitzur Shelah.
109 Kaf Hachaim 131: 34. Mishnah Berurah does not mention that one should recite this verse.
110 Ma’aseh Rav (49). R’ Yosef Shalom Elyashiv and R’ Chaim Pinchas Scheinberg (cited in Tefillah Kehilchashah 15, footnote 14) state that this is the accepted custom.
111 Sha’arei Teshuvah 131:1.
112 Rema 131:1 with Mishnah Berurah, note 9. The Vilna Gaon would recite Shomer Yisrael only on fast days (Ma’aseh Rav 50).
113 See Beiur Halachah 131:1, ד"ה להטות.
114 Ba’eir Heitev 131:2, citing Arizal. The custom of R’ Yisrael Ya’akov Kanievsky was to lean on the lower part of the arm below the elbow (Orchos Rabbeinu I, p. 131 [5774 ed.]); the custom of R’ Ya’akov Kamenetsky was to lean on the upper part of the arm above the elbow (see Emes LeYa’akov 131, footnote 167).
115 Mishnah Berurah 131, note 3.
116 The custom of the Vilna Gaon was to always lean on the left arm (Mishnah Berurah 131, note 6). The custom of R’ Moshe Feinstein was to lean on both arms; see Igros Moshe, Orach Chaim V, 20:19.
117 Shulchan Aruch 131:1 with Mishnah Berurah, note 6. Even if one is wearing tefillin at Minchah, he may lean on his right arm (ibid., note 7).
118 See Pri Megadim, Mishbetzos Zahav 131:2, as well as the letter of R’ Chaim Pinchas Scheinberg printed in Ben Ish Yemini, p. 109.
119 Ben Ish Chai, Ki Sisa 13.
120 Halichos Bas Yisrael 2:12; Machazeh Eliyahu I, 20. See also Emes LeYa’akov 131:1.