Chandogya Upanishad 3.16.3

3.16.3

atha yāni catuścatvāriṃśad varṣāṇi tan mādhyaṃdinaṃ savanam \
catuścatvāriṃśadakṣarā triṣṭup \
traiṣṭubhaṃ mādhyaṃdinaṃ savanam \tad asya rudrā anvāyattāḥ \
prāṇā vāva rudrāḥ \
ete hīdaṃ sarvaṃ rodayanti \\316.3\

3. Now the [next] forty-four years are the mid-day libation,

for the Trishṭubh meter has forty-four syllables and the midday libation is offered with a Trishṭubh hymn. The Rudras are connected with this part of the sacrifice. Verily, the vital breaths are the Rudras, for [on departing] they cause everything here to lament (√ *rud*).