Narrated ibne Abbas (R.A), he said, Rasulullah 9S.A.W) said “No man should stay alone with a women, and no women is allowed to travel on her own except when accompanied by a mehram”. (On hearing this) a man said, “Oh, Messenger of Allah, I have been written in so and so conquest and my wife has already intended for hajj, he (Prophet (S.A.W)) said “go and perform Hajj with your wife”
Abdur Rahman Abul Aswad narrates, “the people of Madinah were ordered to prepare an army and I was also written in for the conquest- thereafter I met Ikrimah the freed slave of Ibne Abbas (R.A), I informed him of my participation.
From the above Ahadeeth it is absolutely clear that before leving fo the path of Allah the names of Sahaba and Tabi’een were written and they used to have registers to write down the names of all the men leaving for conquest.
Tashkeel Book (Register)
Al- Bukhari – Chapter: The narration of Ka’b ibn Malik (R.A) and the statement of Allah Ta’ala: “and Allah (has turned in mercy towards) the tree (Sahba (R.A)) whose matter (of forgiving for not marching to Tabook) was postponed. (the battle of tabook). So the Prophet (S.A.W) announced to the Muslims clearly (their destination). So, that they might get prepared for their ghazwa. So he informed them clearly of the destination he was going to.
Rasulullah (S.A.W) was accompanied by a large number of Muslims who could not be listed in a book namely a register (Tahkeel book)
So many Sahaba went out towards Tabuk that it became hard to even list them down. Inshallah a time will come where there will be extremely lsrge numbers of Muslims in the path of Allah that again it will be hard to list them down.
Again as we can see before going out in the path of Allah, Sahabas names used to be written in registers, just as the tablighee brothers have kept this sunnah alive. That when intentions are made names are written in registers and the amount of time that has been intended and maybe where ever the jamaat will be sent. Jamaats are sent all over the world. Alhamdullilah, and they are sent for I’laae Kalimatillah
(Sahih Al-Bukhari Vol 2 p. 634)