Tosefta zu Tehillim 35:10

Rebbi Meir used to say, ‘It says [in the Torah], “And you should love Hashem, your God, with all of your heart …” (Deuteronomy 6:5) [That means that you should love God] with both of your inclinations, with the good inclination and with the evil inclination. “… and with all of your soul …” (Deuteronomy 6:5) [That means that] even if He takes away your soul [you should still love Him]. And so also it says, “Because for Your sake we are killed all the time …” (Psalms 44:23) [But there is also] another explanation. “With all of your soul” [means] with the soul that He created within you, as it says “Let my soul live and I will praise You …” (Psalms 119:175) And [also] it says, “All my bones will say,’Hashem, Who is like You?”’ (Psalms 35:10)’ Ben Azzai says, “’With all of your soul’ [means that] you should give over your soul to [the performance] of the commandments.”