Brihadaranyaka Upanishad 1.5.17

1.5.17

athātaḥ saṃprattiryadā praiṣyanmanyate'tha putramāha tvaṃ brahma tvaṃ yajñastvaṃ loka iti sa putraḥ pratyāhāhaṃ brahmāhaṃ yajño'haṃ loka iti yadvai kiṃcānūktaṃ tasya sarvasya brahmetyekatā | ye vai ke ca yajñāsteṣām̐ sarveṣāṃ yajña ityekatā ye vai ke ca lokāsteṣām̐ sarveṣāṃ loka ityekataitāvadvā idam̐ sarvametanmā sarvam̐ sannayamito'bhunajaditi tasmātputramanuśiṣṭaṃ lokyamāhustasmādenamanuśāsati sa yadaivaṃvidasmāllokātpraityathaibhireva prāṇaiḥ saha putramāviśati | sa yadyanena kiṃcidakṣṇayākṛtaṃ bhavati tasmādenam̐ sarvasmātputro muñcati tasmātputro nāma sa putreṇaivāsmim̐lloke pratitiṣṭhatyathainamete devāḥ prāṇā amṛtā āviśanti

Now therefore the entrusting: When a man thinks he will die, he says to his son, 'You are Brahman, you are the sacrifice, and you are the world.' The son replies, 'I am Brahman, I am the sacrifice, and I am the world.' (The father thinks:) 'Whatever is studied is all unified in the word "Brahman." Whatever sacrifices there are, are all unified in the word "sacrifice." And whatever worlds there are, are all unified in the word "world." All this (the duties of a householder) is indeed this much. He, being all this, will protect me from (the ties of) this world.' Therefore they speak of an educated son as being conducive to the world. Hence (a father) teaches his son. When a father who knows as above departs from this world, he penetrates his son together with the organ of speech, the mind and the vital force. Should anything be left undone by him through any slip, the son exonerates him from all that. Therefore he is called a son. The father lives in this world through the son. Divine and immortal speech, mind and vital force permeate him.