Śatapatha Brāhmaṇa ("of a hundred paths") 4.5.2.1

4.5.2.1

vaśāmālabhate | tāmālabhya saṃjñapayanti saṃjñapyāha vapāmutkhidetyutkhidya vapāmanumarśaṃ garbhameṣṭavai brūyātsa yadi na vindanti kimādriyeranyadyu vindanti tatra prāyaścittiḥ kriyate

They lay hands on the barren cow, and having laid hands on it, they quiet it. It having been quieted, he says (to the slaughterer), 'Pull out the omentum!' The omentum having been pulled out, let him tell (the slaughterer) to search groping for an embryo. If they do not find one, why need they care? and if they find one, atonement is made therefore.