Mishnah 13 - Chapter 2 - Pirkei Avot

Rabbi shim'on (ben netan'el) omer. Hevei zahir bikri'at shema (uvitfillah). Ucheshe'attah mitpallel, al ta'as tefillatecha keva', ella rachamim vetachanunim lifnei hammakom baruch hu, shenne'emar (vl v) ki channun verachum hu erech appayim verav chesed venicham al hara'ah. Ve'al tehi rasha bifnei atzmach.

Rabbi Shimon said: Be careful with the reading of Shema and the prayer, And when you pray, do not make your prayer something automatic, but a plea for compassion before God, for it is said: “for he is gracious and compassionate, slow to anger, abounding in kindness, and renouncing punishment” (Joel 2:13); And be not wicked in your own esteem.

R. Shimon says: Be heedful of the recitation of the shema [to recite it in its proper time] and of prayer [to recite each prayer in its proper time]. And when you pray, do not make your prayer a rote thing, [thinking to yourself: When can I free myself of this duty? Or: a fixed task, as one who sets himself the task of reciting a chapter or a section (each day), in which instance he makes it mere recitation and not supplication as (does) one who implores mercy], but one's prayer should be (the imploration of) mercy, and supplication before the L rd, as it is written (Yoel 2:13): "For He is a gracious and merciful G-d, withholding wrath and abundant in lovingkindness and repenting Himself of the evil." And do not be wicked to yourself [i.e., do not do something which today or tomorrow will cause you to incriminate yourself. Rambam explains: Do not regard yourself as wicked, for that causes you to become completely corrupt. And I have heard: Do not become wicked in this matter of separating from the congregation (2:4) and being by yourself.]