Shiva Purana
महाकालाभिधस्तातावतारश्शंकरस्य वै ॥ उज्जयिन्यां नगर्य्यां च बभूव स्वजनावनः ॥ १३ ॥
O dear, Śiva incarnated himself as Mahākāla in the city of Ujjayinī for the protection of his devotees.
english translation
mahAkAlAbhidhastAtAvatArazzaMkarasya vai ॥ ujjayinyAM nagaryyAM ca babhUva svajanAvanaH ॥ 13 ॥
hk transliteration by Sanscript