Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/16/37

गर्तात्ततस्समुत्पन्नः शिवो विकटरूपधृक् ।। महाकाल इति ख्यातो दुष्टहंता सतां गतिः ।। ३७।।

sanskrit

From the chasm thus created, Śiva rose up assuming a hideous form. He became famous as Mahākāla, the slayer of the wicked and the goal of the good.

english translation

gartAttatassamutpannaH zivo vikaTarUpadhRk || mahAkAla iti khyAto duSTahaMtA satAM gatiH || 37||

hk transliteration by Sanscript