Skandapurana 5.53.3

5.53.3

vaiśākhyāṃ yo narastatra kṛtvā śrāddhaṃ samāhitaḥ ..
tataḥ paśyati deveśaṃ mahākāla iti smṛtam..
pūjayeddakṣiṇāṃ mūrtiṃ samāśritya dvijottamāḥ .. 3 ..

A man who performs a śrāddha there with a concentrated mind on the full-moon day of Vaiśākha, / and then beholds the Lord of Gods, known as Mahākāla, / should worship him, taking recourse to the southern form, O best of brahmins.