Natyashastra
लिङ्गस्थानां व्रतस्थानां स्थानमेतत्तु कारयेत् । तालास्त्रयोऽर्धतालश्च पादयोरन्तरं भवेत् ॥ ६१॥
This posture is to be used for those of specific sects (liṅgasthāna) and those engaged in religious vows (vratasthāna). The distance between the feet should be three Tālas and a half.
english translation
liGgasthAnAM vratasthAnAM sthAnametattu kArayet । tAlAstrayo'rdhatAlazca pAdayorantaraM bhavet ॥ 61॥
hk transliteration by Sanscript