Sweat of the angels:

The angels release spiritual sweat from their great fear and trepidation of G-d which they experience. This sweat is the source of the water of the river called Nehar Dinor. This river is found between spiritual worlds and serves as a cleansing pool for sinners.[1] This sweat, as all sweat, is the waste of the angels, and is the anger that derives from Kedusha, an anger towards Reshaim who oppose and rebel against Hashem. This is why their sweat serves to create the Dinar river, and is a cleansing pool for Reshaim, a form of Gehinnom.

[1] Torah Or Vayeishev 30b; Siddur Im Dach p. 309a