לָמָּה־לִּ֤י רֹב־זִבְחֵיכֶם֙ יֹאמַ֣ר יְהוָ֔ה שָׂבַ֛עְתִּי עֹל֥וֹת אֵילִ֖ים וְחֵ֣לֶב מְרִיאִ֑ים וְדַ֨ם פָּרִ֧ים וּכְבָשִׂ֛ים וְעַתּוּדִ֖ים לֹ֥א חָפָֽצְתִּי׃
Для чего мне множество ваших жертв? Говорит Господь; Я полон всесожжения баранов и тучных животных животных; И я не наслаждаюсь кровью волов, ягнят или козлов.
Shulchan Arukh, Orach Chayim
One who wants to pray a voluntary prayer needs to know oneself to be quick and careful, and estimate in one's opinion that one will be able to concentrate in one's prayer from beginning to end. But if one is not able to concentrate well, we would consider it [like] "Why do I need all your sacrifices?" (Isaiah 1:11), and [say] would that one could concentrate on the 3 fixed prayers of a day [before trying to do something extra]!