Brihadaranyaka Upanishad 2.1.12

2.1.12

sa hovāca gārgyo ya evāyaṃ chāyāmayaḥ puruṣa etamevāhaṃ brahmopāsa iti sa hovācājātaśatrurmā maitasminsaṃvadiṣṭhā mṛtyuriti vā ahametamupāsa iti sa ya etamevamupāste sarvam̐ haivāsmim̐lloka āyureti nainaṃ purā kālānmṛtyurāgacchati

Gârgya said, 'This being who identifies himself with the shadow, I meditate upon as Brahman.' Ajâtashatru said, 'Please don't talk about him. I meditate upon him as death.' He who meditates upon him as such attains his full term of life in this world, and death does not overtake him before the completion of that term.