There is a famous saying associated with Sri Vidya which goes like this:
"Your head can be given, your soul can be given but the Shodashi Vidya of the Devi can not be given"
Here reference is to a powerful and secret mantra of Mother Goddess.
Recently, i have found the original sloka, translation of which is the above saying.
AsyA MahAtyamtulam Jihvakotisatairapi | Vaktum Na Sakyate Devi Kim Punah Panchabhinarmukhaih || Api Priyatamam Deyam SutadAradhanAdhikam | Rajyam Deyam Siro Deyam Na Deyo ShodhashAkshari ||
[Lord Shiva says to Devi] Its unmatched greatness can not be described even if someone has hundred crores of tongues. How can my five faces describe its greatness then? The most loved objects of someone, son, wife, wealth, kingdom and even one's head can be given, but shodakshari can't be given
By studying the verses that are found along with these verses, i am guessing that the verses are from one of the Yamala Texts (like Rudra Yamala, Brahma Yamala, Vishnu Yamala etc). Or it can be present in some other Agamas as well.
Question- Which Agama is the source of the verses in question?