Matsya Purana 261.24

261.24

tathaiveśaṃ pravakṣyāmi dhavalaṃ dhavalekṣaṇam.
triśūlapāṇinaṃ devaṃ tryakṣaṃ vṛṣagataṃ prabhum .. 261.23

The image of Lord Iśâna should be made white with white eyes, armed with a trident, having three eyes, riding on a bull—23