Walima’ is the wedding feast which is to be given by the groom to all after his marriage. Following hadith (and there are other narrations also on the subject) confirms that ‘Walima’ is obligatory:
Anas bin Malik (RA) narrated: Allah’s Messenger (PBUH) saw some traces of saffron on Abdur-Rahman bin Awf (RA), so he said, “What is this?” he said, “I married a woman for the amount of gold equal to a date stone.” So he said, “May Allah bless you. Have a banquet (i.e. a wedding feast; a ‘Walima’), even if with only one sheep.”
(Hadith No. 1094, Chapters on Marriage, Jami’ At-Tirmidhi, Vol. 2; Hadith No. 1907, Chapters on Marriage, Sunan Ibn Majah, Vol. 3).
“On the authority of Asmaa’ bint Yazid who narrated “that she was once in the presence of the Prophet and there were both men and women sitting. The Prophet then said: “Perhaps a man might discuss what he does with his wife, or perhaps a woman might inform someone what she did with her husband?” The people were silent. Then I said: “O, Yes! O Messenger of Allah verily both the women and men do that.” Then the Prophet said: “Do not do that. It is like a male Satan who meets a female Satan along the way, and has sex with her while the people look on! ”
[Reported by Ahmad]