Rashi on Exodus 18:23/רש"י על שמות י״ח:כ״ג

1וצוך אלהים ויכלת עמד This implies: Consult the Almighty; if He commands thee to do this, thou wilt be able to stand, and if He prevents thee thou wilt be unable to stand (Mekhilta).

2וגם כל העם הזה AND ALL THIS PEOPLE ALSO — Aaron, Nadab and Abihu and the seventy elders who are now associated with you (Mekhilta).