Agniveshyagrihyasutra 2.6.8.30

2.6.8.30

ityāvāhya oṃ bhūḥ oṃ bhuvaḥ oṃ suvaḥ oṃ mahaḥ oṃ janaḥ oṃ tapaḥ oṃ satyaṃ oṃ tatsaviturvareṇyaṃ bhargo devasya dhīmahi dhiyo yo naḥ pracodayāt ityetamanuvākaṃ trirabhyasya trīn prāṇāyāmān dhārayitvā nakṣatrāṇāmudayāt pūrvaṃ praṇavena vyāhṛtībhiḥ saha sāvitrīṃ sahasrakṛtva āvartayet śatakṛtvo vā daśāvaraṃ vā \

Having thus invoked, having repeated three times this anuvāka: "Om bhūḥ, Om bhuvaḥ, Om suvaḥ, Om mahaḥ, Om janaḥ, Om tapaḥ, Om satyam; Om, may we meditate on that desirable splendor of the divine Savitṛ, who shall inspire our thoughts," having performed three breath controls, before the rising of the stars he should repeat the Sāvitrī together with the sacred syllable Om and the mystic utterances a thousand times, or a hundred times, or at least ten times.