Adam Clarke on Hebrews 11:8

Abraham, when he was called - See on Gen 12:1-4 (note).

Not knowing whither he went - Therefore his obedience was the fullest proof of his faith in God, and his faith was an implicit faith; he obeyed, and went out from his own country, having no prospect of any good or success but what his implicit faith led him to expect from God, as the rewarder of them that diligently seek him. In all the preceding cases, and in all that follow, the apostle keeps this maxim fully in view.