Anandakanda 1.21.44

1.21.44

likhedbhūpurakoṇeṣu ṭhakārāndikṣu vinyaset /
idaṃ hi mātṛkāyantraṃ viṣamṛtyugadāpaham //

One should write [these], and place the syllable “ṭha” in the corners of the bhūpura and in the cardinal directions. / This indeed is the Mātṛkā yantra, which removes poison, death, and disease.