Skandapurana 5.36.51

5.36.51

tato bhavati saṃsiddho maṃtrārhaḥ sa naraḥ śuciḥ ..
japedbrāhmaṇaśārdūla tato lakṣacatuṣṭayam ..
daśāṃśena tu homaḥ syātsusamiddhe hutāśane .. .. 51 ..

Then, purified, that man becomes accomplished and worthy of the mantra. / Then he should recite it four hundred thousand times, O tiger among brahmins; / and one-tenth of that should be an oblation offered into a well-kindled fire.