Praise be to Allah.
According to sharee’ah, marriage is done through the contract between the two spouses, with the consent of the woman’s guardian and in the presence of two witnesses. Such a contract is complete even if there is no celebration or party. See question no. 2127.
With regard to the celebration of the marriage, announcing it and inviting people to a feast on this occasion as an expression of joy and to publicize the marriage, all of these are things which are mustahabb (encouraged) on the occasion of marriage. The Prophet (peace and blessings of Allaah be upon him) said: “Announce marriage.” (Narrated by Ahmad, 4/5; classed as saheeh by al-Haakim, 2/200; classed as hasan by al-Albaani in Saheeh al-Jaami’, 1072).
And the Prophet (peace and blessings of Allaah be upon him) said to ‘Abd al-Rahmaan ibn ‘Awf when he got married, “Give a feast, even with one sheep.” (Narrated by al-Bukhaari, 1943; Muslim, 3475).
See al-Mughni, 8/105.