Reference for Psalms 18:31

הָאֵל֮ תָּמִ֪ים דַּ֫רְכּ֥וֹ אִמְרַֽת־יְהוָ֥ה צְרוּפָ֑ה מָגֵ֥ן ה֝֗וּא לְכֹ֤ל ׀ הַחֹסִ֬ים בּֽוֹ׃

As for God, His way is perfect; the word of the LORD is tried; He is a shield unto all them that take refuge in Him.

ספר השרשים