Skandapurana 5.30.17

5.30.17

yo me liṃgasya yāmyāśāṃ sthitvā maṃtraṃ japiṣyati ..
ṣaḍakṣaraṃ pradāsyāmi tasyāyuṣyaṃ sutānvitam .... .. 17 ..

Whoever, standing in the southern direction of my liṅga, will recite the mantra / of six syllables, to him I will give long life accompanied by sons.”