Hakim al Ummah Maulana Ashraf Ali Thanwi (Allah have mercy on him) instructed,

The biayah (spiritual convent or pact) with the women must not be done by holding their hands in one’s hand.
The Prophet (Allah bless him and grant him peace) never ever touched a woman while taking biayah.
It is impermissible (haram) to touch a non-mehram female.
The author of ‘Mehboob us Salikeen’ writes, ‘the biayah of female is as follows, if they are not (physically) present there then they should be inducted via a (mehram) relative and the instructions regarding the biayah conveyed to them by this representative. Moreover, the Shaykh may gift them a piece of his clothing (as reminder). However, if the woman is present then their biayah must be from behind a veil, and not by holding their hands.

Taleem ud Deen p192-3