Listen to the twenty-first shloka, first chapter of the Hatha Yoga Pradipika:
जानूर्वोर् अन्तरे सम्यक् कृत्वा पादतले उभे ।
ऋजुकायः समासीनः स्वस्तिकं तत् प्रचक्षते ॥२१॥
jānu-ūrvor antare samyak kṛtvā pāda-tale ubhe |
ṛju-kāyaḥ samāsīnaḥ svastikaṁ tat pracakṣate ||21|
For more Information, including the Sanskrit text in Devanagari and Roman script, go to the Hatha Yoga Pradipika Page on Hatha Yoga Pradipika I 21.