מַה־תִּשְׁתּ֬וֹחֲחִ֨י ׀ נַפְשִׁי֮ וַתֶּהֱמִ֪י עָ֫לָ֥י הוֹחִ֣ילִי לֵֽ֭אלֹהִים כִּי־ע֥וֹד אוֹדֶ֗נּוּ יְשׁוּע֥וֹת פָּנָֽיו׃
Why art thou cast down, O my soul? And why moanest thou within me? Hope thou in God; for I shall yet praise Him for the salvation of His countenance.
Read halakhic rulings (Jewish law) on Psalms 42:6: and classical halakhic sources.