Khândogya Upanishad: II, 3

THIRD KHANDA. 1. Let a man meditate on the fivefold Sâman as rain. The hiṅkâra is wind (that brings the rain); the prastâva is, 'the cloud is come;' the udgîtha is, 'it rains;' the pratihâra, 'it flashes, it thunders;' 2. The nidhana is, 'it stops.' There is rain for him, and he brings rain for others who thus knowing meditates on the fivefold Sâman as rain.