SB 8.18.14

tasyopanīyamānasya
 sāvitrīṁ savitābravīt
bṛhaspatir brahma-sūtraṁ
 mekhalāṁ kaśyapo ’dadāt
Word for word: 
tasya — of Lord Vāmanadeva; upanīyamānasya — at the time of His being offered the sacred thread ceremony; sāvitrīm — the Gāyatrī mantra; savitā — the sun-god; abravīt — chanted; bṛhaspatiḥ — Bṛhaspati, the guru of the demigods; brahma-sūtram — the sacred thread; mekhalām — the belt of straw; kaśyapaḥ — Kaśyapa Muni; adadāt — offered.
Translation: 
At the sacred thread ceremony of Vāmanadeva, the sun-god personally uttered the Gāyatrī mantra, Bṛhaspati offered the sacred thread, and Kaśyapa Muni offered a straw belt.