Pierkei Avot - Chapter 2 Mishna 18b
"Rabbi Shimon said: Be careful with the recitation of the Shema and the prayers. When you pray, do not regard your prayers as a fixed obligation but rather as the asking for mercy and supplication before G-d, as the verse states, 'For gracious and merciful is He, slow to anger, great in kindness, and relenting of the evil decree' (Joel 2:13).

Do not consider yourself wicked in your own eyes."