He was punished by his posterity being compelled to serve the Egyptians two hundred and ten years, because he had pressed the Rabbis under his tuition into military service in the expedition he had undertaken to recover Lot from those who had carried him off captive; for it is written (Gen. xiv. 14), " He armed his instructed." Samuel says Abraham was punished because he perversely distrusted the assurance of God; as it is written (Gen. xv. 8), "Whereby shall I know that I shall inherit it? ■
Why Abraham's Children Served Egypt Two Hundred Years
Nedarim 31b (via Hebraic Literature, 1901)