Talmud for Pirkei Avot 5:23
בֶּן הֵא הֵא אוֹמֵר, לְפוּם צַעֲרָא אַגְרָא:
Ben Ha Ha says: According to the suffering is the reward. [The more "suffering" that you invest in toiling in Torah study and in doing mitzvoth, the greater will be your reward.]
Avot D'Rabbi Natan
Rabbi Yehudah ben Teima would say: Be strong like a leopard, light like an eagle, fast like a deer, and brave like a lion in doing the will of your Father in heaven.
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