Kautilya's Arthashastra 14.2.5

14.2.5

takrayavabhakṣasya saptarātrād ūrdhvaṃ śvetagardabhasya leṇḍayavaiḥ siddhaṃ gaurasarṣapatailaṃ virūpakaraṇam //

The oil extracted from white mustard seeds mixed with the barley-corns contained in the dung of a white donkey, which has been living for more than seven nights on a diet of butter, milk and barley, causes alteration in colour.