Śatapatha Brāhmaṇa ("of a hundred paths") 3.3.4.10

3.3.4.10

palāśaśākhayā prājati | yatra vai gāyatrī somamacāpatattadasyā āharantyā apādastābhyāyatya parṇam praciceda gāyatryai vā somasya vā rājñastatpatitvā parṇo 'bhavattasmātparṇo nāma tadyadevātra somasya nyaktaṃ tadihāpyasaditi tasmātpalāśaśākhayā prājati

He drives with a palâsa branch. Now when Gâyatrî flew towards Soma, a footless archer aiming at her while she was carrying him off, severed one of the feathers (or leaves, parna), either of Gâyatrî or of king Soma; and on falling down it became a parna (palâsa) tree; whence its name parna. 'May that which was there of the Soma nature, be here also now!' so he thinks, and for this reason he drives with a palâsa branch.