Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.3.9

1.4.3.9

śociṣkeśastamīmaha iti | śiśnaṃ vai śociṣkeśaṃ śiśnaṃ hīdaṃ śiśnam bhūyiṣṭhaṃ śocayati śiśnamevaitayāsaminddhe 1.4.3[.1]0 samiddho agna āhuteti | ya evāyamavāṅprāṇa etamevaitayā saminddha ā juhotā duvasyateti sarvamātmānaṃ saminddha ā nakhebhyo 'tho lomabhyaḥ

Further, 'The flaming-locked, him we adore!' the flaming-locked, doubtless, is the sisna, for it is that organ which chiefly burns (torments) him who is endowed with it: the sisna he accordingly kindles by this (the ninth verse).