The first elaborate description of Upanayana Sanskar is found in the

Solution (By Examveda Team)

Tandya Mahabrahmana or Panchavimsa Brahmana belongs to both Kauthuma and Ranayaniya Shakha of the Samaveda. It is consisting of twenty-five prapathakas and 347 khandas. Tandya Brahmana describes about Jyotishtoma, Ukthya, Atiratra, Prakrtis of ekahas and ahinas, Somaprayaschittas, Dvadashaha rite, collection of Yajus and Vistutis. It is famous for ancient legends. According to Samavidhana Brahmana, this work is ascribed to Acharya Tandi.