Mubāyaʿa (mutual pledge of allegiance) refers to the handshake (musāfaḥa) and agreement made when entering a tariqa (a Sufi path/order). The murīd (aspirant, disciple) sits before the shaykh and listens to the requirements of the tariqa from him. Based on this meaning, the phrase "So-and-so took a covenant" means that he pledged to fulfill the requirements of the tariqa and to obey the commands of his shaykh. (Rihle, 247)
Mubāyaʿa is from the world of spirits (rūḥlar ʿālemi). The spirits (arwāḥ) of the murīds are connected to the spirit (rūḥ) of the shaykh. In the world of spirits, the spiritual presence (rūḥāniyya) of the shaykh watches over the murīd. When the murīd enters the physical world, the shaykh's spiritual presence continues to watch over him, and until he comes and makes the mutual pledge of allegiance, a cause is gradually created to bring him closer to his shaykh. (Nafahāt, 125)