Yaakov 1:6-8

Orthodox Jewish Bible

⁶ But let the tefillah be offered with much bitachon in emunah (faith), in no way doubting. For the doubtful man, wavering in emunah, is like a wave of the yam (sea) being tossed by the wind. [MELACHIM ALEF 18:21]

⁷ Let not such a one presume that he will receive anything from Adoneinu.

⁸ He is an ish (man) of double mind, in all his drakhim (ways), mesupak (uncertain, having doubts) and unstable. [TEHILLIM 119:113]