תניא, חלק ראשון; ליקוטי אמרים כ״ח — ד"ה וַאֲפִילוּ אִם נוֹפְלִים לוֹ הִרְהוּרֵי תַּאֲווֹת
Explains how intrusive thoughts and worldly burdens can pull a person away from focused service, and how one should respond without despair.
וַאֲפִילוּ אִם נוֹפְלִים לוֹ הִרְהוּרֵי תַּאֲווֹת וּשְׁאָר מַחֲשָׁבוֹת זָרוֹת בִּשְׁעַת הָעֲבוֹדָה בַּתּוֹרָה אוֹ בִּתְפִלָּה בְּכַוָּונָה, אַל יָשִׁית לֵב אֲלֵיהֶן, אֶלָּא יַסִּיחַ דַּעְתּוֹ מֵהֶן כְּרֶגַע. אַךְ אַף־עַל־פִּי־כֵן, אַל יִפּוֹל לִבּוֹ בְּקִרְבּוֹ לִהְיוֹת מִזֶּה עָצֵב נִבְזֶה בִּשְׁעַת הָעֲבוֹדָה, שֶׁצָּרִיךְ לִהְיוֹת בְּשִׂמְחָה רַבָּה, אֶלָּא אַדְּרַבָּה, יִתְחַזֵּק יוֹתֵר וְיוֹסִיף אוֹמֶץ בְּכָל כֹּחוֹ בְּכַוָּונַת הַתְּפִלָּה בְּחֶדְוָה וְשִׂמְחָה יְתֵירָה, בְּשׂוּמוֹ אֶל לִבּוֹ, כִּי נְפִילַת הַמַּחֲשָׁבָה זָרָה הִיא מֵהַקְּלִיפָּה שֶׁבֶּחָלָל הַשְּׂמָאלִי, הָעוֹשָׂה מִלְחָמָה בְּבֵינוֹנִי עִם נֶפֶשׁ אֱלֹהִית שֶׁבּוֹ. וְאִם יִקְשֶׁה לוֹ לַהֲסִירָם מִדַּעְתּוֹ, מִפְּנֵי שֶׁטּוֹרְדִים דַּעְתּוֹ מְאֹד בְּחָזְקָה – אֲזַי, יַשְׁפִּיל נַפְשׁוֹ לַה׳ וְיִתְחַנֵּן לוֹ יִתְבָּרֵךְ בְּמַחֲשַׁבְתּוֹ, לְרַחֵם עָלָיו בְּרַחֲמָיו הַמְרוּבִּים, כְּרַחֵם אָב עַל בָּנִים הַנִּמְשָׁכִים מִמּוֹחוֹ, וְכָכָה יְרַחֵם ה׳ עַל נַפְשׁוֹ הַנִּמְשֶׁכֶת מֵאִתּוֹ יִתְבָּרֵךְ, לְהַצִּילָהּ מִ״מַּיִם הַזֵּדוֹנִים״, וּלְמַעֲנוֹ יַעֲשֶׂה, ״כִּי חֵלֶק ה׳״ – מַמָּשׁ – ״עַמּוֹ״:
Even if there occur to him lustful imaginations or other extraneous thoughts during Divine service, in Torah or in devout prayer, he must not let his heart dwell on them but must immediately avert his mind from them. Nevertheless he must not be downcast at heart and feel dejected and despicable during Divine service, which should be with great joy. On the contrary, he should draw fresh strength and intensify [his] effort with all his power to concentrate on the prayer with increased joy and gladness in the realization that the foreign thought that had invaded his heart comes from the kelipah in the left part, which, in the case of the benoni, wages war with the divine soul within him. However, if he finds it hard to dismiss them from his mind, because they distract his mind with great intensity, then he should humble his spirit before G–d and supplicate Him in his thought to have compassion upon him in His abundant mercies, as a father who takes pity on his children who stem from his brain; so may G–d have pity on his soul which is derived from Him Who is blessed and deliver it from the “turbulent waters”; for His sake He will do it, for verily “His people is a part of the L–rd.”