Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.4.8

13.4.4.8

atha yatkuntāpamāsīt yo majjā sa sārdhaṃ samavadrutya śrotrata udabhinatsa eṣa vanaspatirabhavadbilvastasmāttasyāntarataḥ sarvameva phalamādyam bhavati tasmādu hāridra iva bhavati hāridra iva hi majjā tenaivainaṃ tadrūpeṇa samardhayatyantare paitudāruvau bhavato bāhye bailvā antare hi cakṣuṣī bāhye śrotre sva evaināṃstadāyatane dadhāti

And what 'kuntâpa,' what marrow there was, that flowed together, and burst forth from the ear, and became that tree, the bilva; whence all the fruit of that (tree) is eatable inside, and whence it (the tree, or wood) is yellowish, for marrow is yellowish: with that quality he thus endows it. The two (sets of) pîtudâru (stakes) stand inside, and the bilva ones outside, for the eyes are inside, and the ears outside: he thus puts them in their own place.