(Qur’an...
(Qur’an, Surah Fath 48:10) This verse also proves that Bayyat and Mubaiya both imply the same ledge and vow with Allah and His Messenger, and those who fulfill this pledge are promised a great reward.
This Bayyat can be established in two steps: Firstly: Making a firm intention to be steadfast in obeying the command of Imam (as) and helping him; and sacrificing ones life and property for him as mentioned in the holy verse: “Surely Allah has bought of the believers their persons and their property for this…” Now it is obligatory on the seller to hand over without any delay, what he has sold to the buyer whenever the latter demands it and that which is in his mind will be revealed.
Secondly: What he has in his mind and that which he has decided should be at the same time expressed verbally and in this manner the Bayyat will take place, just as the formula of sale and purchase and other transactions is not complete except through two steps: One: An intention and determination to undertake that transaction as per the agreement of the buyer and seller; and Two: To recite all this verbally; and only after that is the transaction complete.
Sometimes Bayyat is also performed by putting of ones hand over that of the other as was customary among the Arabs and this is according to the saying of the Almighty: One who does Bayyat to you, has in fact done Bayyat to Allah. Allah’s hand is upon his hand. Moreover, companions of the Messenger of Allah (S) used to place their hands in the hand to give Bayyat.
In Ihtijaj it is mentioned in the incident in which our master, Amirul Momineen (as) was forced to do the Bayyat to the first usurper of caliphate as follows: Then they pulled the hand of His Eminence [Amirul Momineen (as)], while he was holding it back, but they pulled by force and putting it over the hand of Abu Bakr said: Do the Bayyat. Do the Bayyat.
And the call echoed in the Masjid: Abul Hasan has done the Bayyat, done the Bayyat… Also in Ihtijaj it is mentioned in the traditional report of our master His Eminence, Baqir (as) that he said: When Usamah entered Medina and saw that people had joined on the Bayyat of Abu Bakr, he went to Ali Ibne Abi Talib (as) and said to His Eminence: What is this? Ali (as) replied: It is as you see! Usamah asked: Have you done Bayyat to him? He replied: Yes, O Usamah.