Sheikh Fawzān ḥafidhahullāh:

“This person is asking about a marriage contract without official papers. If the conditions for the marriage contract are met; namely, presence of a guardian, two just witnesses, mutual consent from both spouses...then the contract is valid - even if it is not documented in the official departments. This (documentation) is only a procedure! Documentation through official departments is good; because they will not help you in your affairs except with a marriage certificate. This document is necessary, but the marriage itself, if its conditions are met [then it is valid], but there remains for you to complete the procedure required of you for your own sake. But it is better for you to follow the regular procedure from the onset. That is better than you getting married without documentation and then going to try and officialise it afterwards, perhaps they won't endorse it, and you put yourself in difficulty. So it is better to stick to the regular procedure.