The Compendium of Caraka 1.11.15

1.11.15

nāstikasyāsti naivātmā yadṛcchopahatātmanaḥ /
pātakebhyaḥ paraṃ caitat pātakaṃ nāstikagrahaḥ //

nor does a self exist at all for the atheist whose soul is destroyed by belief in chance; / and of all sins, this clinging to atheism is the worst sin.