Chandogya Upanishad
Prapathaka II, Khanda 7
Let a man meditate on the fivefold Sâman, which is greater than great, as the prânas (senses). The hiṅkâra is smell (nose), the prastâva speech (tongue), the udgîtha sight (eye), the pratihâra hearing (ear), the nidhana mind. These are one greater than the other.