Chapter 3 · verse 38 · gita.yoga.org

Bhagavad Gita 3.38

धूमेनाव्रियते वह्निर्यथाऽऽदर्शो मलेन च। यथोल्बेनावृतो गर्भस्तथा तेनेदमावृतम्

As fire is enveloped by smoke, as a mirror is covered by dust, and as an embryo is surrounded by the amniotic sac, so is this enveloped by that.