Gyaneshwari -Sant Gyaneshwar
When he becomes seated and his activity ceases, he easily achieves concentration and becomes proficient in Yoga. I shall now describe to you an excellent mudra. First he should sit folding the legs on the corresponding thighs placing the left leg obliquely over the right. Then pressing firmly the right heel against the sphincter of the anus, and keeping it on the ground, he should press it against the pubic bone so that the right heel perches on the left heel. Of the space of four fingers between the anus and the male organ he should leave the space of one and half fingers above and below (191-195)
and press by the upper part of the heel the middle space one finger wide. Then balancing the body, as if lifting the lower part of the spinal column, he should keep the two ankles straight. Now the whole body, O Partha, remains steady on the two heels, Arjuna, this is the characteristic of the mudra known as mulabandha, also known as vajrasana, the diamond posture. When he achieves this mudra, the in-breath, with its downward passage blocked, begins to move backwards (196-200).