Brihadaranyaka Upanishad 1.7

तं जातमभिव्याददात् । स भाणकरोत् । सैव वागभवत् ॥

tam jatam abhivyadadat | sa bhan akarot | saiva vag abhavat ||

When the child was born, he (Death) opened his mouth to swallow it. The child cried 'Bhan!' — and that indeed became speech.

जन्म लेते ही उसने (मृत्यु ने) उसे निगलने के लिए मुँह खोला। उसने 'भाण्' शब्द किया। वही वाक् बन गई।