לָמָּה־לִּ֤י רֹב־זִבְחֵיכֶם֙ יֹאמַ֣ר יְהוָ֔ה שָׂבַ֛עְתִּי עֹל֥וֹת אֵילִ֖ים וְחֵ֣לֶב מְרִיאִ֑ים וְדַ֨ם פָּרִ֧ים וּכְבָשִׂ֛ים וְעַתּוּדִ֖ים לֹ֥א חָפָֽצְתִּי׃
여호와께서 말씀하시되 너희의 무수한 제물이 내게 무엇이 유익하뇨 나는 수양의 번제와 살진 짐승의 기름에 배불렀고 나는 수송아지나 어린 양이나 수염소의 피를 기뻐하지 아니하노라
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]!