Śatapatha Brāhmaṇa ("of a hundred paths") 14.2.2.46

14.2.2.46

taṃ na sarvasmā iva pravṛñjyāt sarvam vai pravargyo netsarvasmā iva sarvaṃ karavāṇīti yo nveva jñatastasmai pravṛñjyādyo vāsya priyaḥ syādyo vānūcāno'nūktenainam prāpnuyāt

Let him not perform the Pravargya for any and every one, lest he should do everything for every one, for the Pravargya is everything; but let him only perform it for him who is known, or to whoever may be dear to him, or who has studied sacred writ: by means of the study of sacred writ he would thus gain it.