Where is the mind referred to as being luminous? I recall the natural state of mind being referred to as luminous somewhere in Buddhist canonical texts. I've always been very taken with that imaginary. I'm sure it's quite a common image in the texts but can anyone give me one or two examples of it. Also is this concept/image linked to the notion of Buddha Nature in some way?
The earliest reference is from the Pali Tipitaka, AN 5.49-50:

49. “pabhassaramidaṃ, bhikkhave, cittaṃ. tañca kho āgantukehi upakkilesehi upakkiliṭṭhan”ti.
50. “pabhassaramidaṃ, bhikkhave, cittaṃ. tañca kho āgantukehi upakkilesehi vippamuttan”ti.
Luminous, o Bhikkhus, is this mind. And indeed by those invading defilements it is defiled.
Luminous, o Bhikkhus, is this mind. And indeed from those invading defilements it is released.