Chandogya Upanishad 2.3.1

2.3.1

vṛṣṭau pañcavidhaṃ sāmopāsīta \
purovāto (S )kāraḥ \
megho jāyate sa prastāvaḥ \
varṣati sa udgīthaḥ \
vidyotate stanayati sa pratihāraḥ \
udgṛhṇāti tan nidhanam \\203.1\

1. In a rain-storm one should reverence a fivefold Sāman. The preceding wind is a Hiṅkāra. A cloud is formed—that is a Prastāva. It rains—that is an Udgītha. It lightens, it thunders—that is a Pratihāra.

2. It lifts—that is a Nidhana. It rains for him, indeed, he causes it to rain, who, knowing this thus, reverences a fivefold Sāman in a rain-storm.