Chandogya Upanishad
Prapathaka V, Khanda 16
Then he said to Budila Âsvatarâsvi, 'O Vaiyâghrapadya, whom do you meditate on as the Self?' He replied: 'Water only, venerable king.' He said; 'The Self which you meditate on is the Vaisvânara Self, called Rayi (wealth). Therefore are you wealthy and flourishing.