In order to carry out a temporary (concubine) marriage contract, a number of prerequisites ought to be executed:
(i) the contract's formula ought to be read out. Consent (from the man and woman involved), alone, does not suffice; such a consent, moreover, must be accompanied by a declaration of specific and stipulated phrases.
(ii) Obligatory precaution dictates that the contract's wording be recited accurately in Arabic. Assuming the man and woman are not able to recite the formula, in Arabic, it won't be necessary to execute the contract by proxy; reciting the contract in another language is deemed valid. All that is required is that the meaning of the terms 'zawwaj-tu' (I have married) and 'qabil-tu' (I have accepted) be properly conveyed and understood.
(iii) Assuming the man and woman desire to execute the contract by themselves, they must initially stipulate the temporary marriage's (a) time frame (e.g. 1 hour, 2 days, 3 months etc.) and (b) dowry. Next, the woman must recite:
"zawwaj-tu-ka nafsi fil-mudda-til ma'loomah 'alal mah-ril ma'loom"
[I have married myself to thee (or I wed myself to thee) with respect to the stipulated time frame and over the stipulated dowry]
The man must follow successively by saying:
"qabil-tu" [I have accepted]
Another variation involves the woman's attorney saying (to the man's attorney):
"matta'-tu muwakkilati muwakkila-ka fil-mudda-til ma'loomah 'alal mah-ril ma'loom"
[I have married my client to your client with respect to the stipulated time frame and over the stipulated dowry]
The man's attorney then follows successively by saying:
"qabil-tu li-muwakkili haakatha" [I have accepted this for my client]
(iv) The determination, and stipulation, of the dowry ought to be done at the time of the contract's execution.
(v) Note that the man and woman, or their attorneys, must intend to 'declare' their marriage contracts i.e. by reciting "zawwaj-tu-ka nafsi…" the woman ought to intend to declare that she is designating herself as the man's wife; and by reciting "qabil-tu", the man must intend to declare acceptance vis-à-vis the woman's being his wife
(vi) The one who recites the contract formula ought to be sane and pubescent.
(vii) Assuming the man and woman's attorneys or guardians are carrying out the contract, the man and woman's names ought to be specified
(viii) A pubescent virgin requires her father/grandfather's permission in order to marry, even though she is autonomous (i.e. able to lead her life independently). However, such permission is not required were she not a virgin (due to a previous husband).
(ix) At the time of the contract's execution, the woman must neither be, actually, temporarily/permanently married to another nor be within her 'iddah (i.e. the period during which she must wait after divorce or death of her husband before she may legitimately re-marry)
(x) Consent is necessary; any form of compulsion or force is prohibited.
Naturally, there exists other matters and conditions which may be accessed in books of jurisprudence. The above information is in accordance with the verdicts of Imam Khumayni; if your religious authority is someone else, please inform us and we shall reply accordingly.