Kautilya's Arthashastra 14.3.69

14.3.69

kṛṣṇacaturdaśyāṃ śastrahatāyā goḥ kapilāyāḥ pittena rājavṛkṣamayīm amitrapratimām añjyāt, andhīkaraṇam //

When the figure of an enemy carved out of rájavriksha (cassia fistula) is besmeared with the bile of a brown cow killed with a weapon on the fourteenth day of the dark half of the month, it causes blindness (to the enemy).