Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Marriage, according to Islam, is a solemn social contract. Since it is not a secret liaison between man and woman, it cannot remain a secret affair; rather it should be publicized so that people recognize them as a married couple.
The Prophet (peace be upon him) is reported to have said,
“Publicize marriage and beat drums to celebrate it.” (Ibn Majah)
Now, what is an acceptable form of marriage varies from culture to culture. In advanced societies, marriages are documented and solemnized according to legal requirements, the purpose of which is to preempt any potential disputes.
Since the Shariah laws are based on higher objectives and purposes, including protection of honor, strengthening the family, etc., it is only reasonable to think that marriages should be documented – as per the requirements of the country.
In conclusion, registering marriage is highly crucial to safeguard the interests of marriage partners.
Almighty Allah knows best.