Śatapatha Brāhmaṇa ("of a hundred paths") 4.5.2.4

4.5.2.4

taṃ niruhyamāṇamabhimantrayate | ejatu daśamāsyo garbho jarāyuṇā saheti sa yadāhaijatviti prāṇamevāsminnetaddadhāti daśamāsya iti yadā vai garbhaḥ samṛddho bhavatyatha daśamāsyastametadapyadaśamāsyaṃ santam brahmaṇaiva yajuṣā daśamāsyaṃ karoti

When it is pulled out, he addresses it with (Vâg. S. VIII, 28), 'May the embryo of ten months move together with the caul!'--by saying, 'May it move,' he puts breath into it; and 'of ten months' he says, because when an embryo is full grown, then it is one of ten months: thus, even though it is not ten months old, he makes it one of ten months by means of the Brahman (prayer), the Yagus.