The Marriage Banquet (Walima):

After the consummation of the marriage, the groom holds a banquet called a walima. The relatives, neighbors, and friends are invited in order to make them aware of the marriage. Both rich and poor of the family and community are invited to the marriage feasts.

Prophet Muhammad (S) said:

'The worst of the feasts are those marriage feasts to which the rich are invited and the poor are left out". (Mishkat)

It is recommended that Muslims attend marriage ceremonies and marriage feasts upon invitation.

Prophet Muhammad (S) said:

"...and he who refuses to accept an invitation to a marriage feast, verily disobeys Allah and His Prophet". (Ahmad & Abu Dawood)

Narrated Anas: When 'Abdur-Rahman came to us, the Prophet established a bond of brotherhood between him and Sa'd bin Ar-Rabi'. Once the Prophet said, "As you (O 'Abdur-Rahman) have married, give a wedding banquet even if with one sheep." '"
[Bukhari]

Narrated Abu Musa: "The Prophet, peace be upon him, said, `Set the captives free, accept the invitation (including to a wedding banquet), and pay a visit to the patients.'"
[Bukhari]

By this saying of the Prophet, peace be upon him, it is also enjoined upon us to join in the happiness of our brothers