Moment of joys are common to all peoples. From birth to marriage and very many other reasons to feel light hearted. It is common to share these joys with people through easting (waleemah). Inviting people tofeast and accepting it is a matter that is guided in Islam. The following is a summary of this guidance.
It is compulsory to accept invitation
Allaahs Messenger (salalahu alayhi wa sallam) said, "If anyone of you is invited to a wedding banquet, he must go for it (accept the invitation)." (Bukhari)
Reject invitation to a feast where there is sinfulness
Reported Ali ibn AbiTalib (RA):"I prepared meal and invited the Messenger of Allaah (salalahu alayhi wa sallam). He came and saw some pictures in the house;then he turned back. I said to him May my father and mother be your ransom, what prevented you? He said: There is a curtain containing pictures in the house and angels do not enter a house in which there are pictures." (Ibn Majah) Do not invite only the rich The Rasul (salalahu alayhi wa sallam) said: "The worst food is that of a wedding banquet to which only the rich are invited while the poor are not invited. And he who refuses an invitation (to a banquet) disobeys Allaah and His Messenger." (Bukhari) ... even if you are fasting Abdullah bin Umar (RA) said, "Allaahs Messenger (salalahu alayhi wa sallam) said, "Accept the marriage invitation if you are invited to it." Ibn Umar used to accept the invitation whether to a wedding banquet or to any other party, even when he was fasting. (Bukhari) Only the invited may attend An Ansari man, called Abu Shuaib, came and told his butcher slave, "Prepare meals sufficient for five persons, for I want to invite the Prophet along with four other persons as I saw signs of hunger on his face." Abu Shuaib invited them and another person came along with them. The Prophet said (to Abu Shuaib), "This man followed us, so if you allow him, he will join us, and if you want him to return, he will go back." Abu Shuaib said, "No, I have allowed him (i.e. he, too, is welcomed to the meal)." (Bukhari)
Do not look down on your host's meal
The Prophet (salalahu alayhi wa sallam) said, "I shall accept the invitation even if I were invited to a meal of a sheep's trotter, and I shall accept the gift even if it were an arm or a trotter of a sheep." (Bukhari). If its voluntary fast, then there is a choice Allaahs Messenger (salalahu alayhi wa sallam) said: "If anyone of you is invited, he should accept (the invitation) In case he is fasting he should pray (in order to bless the inmates of the house) and ifhe is not fasting he should eat." (Muslim)
However, do not turn back those who come Allaahs Prophet (salalahu alayhi wa sallam) said: "The worst kind of food is at the wedding feast from which one who comes is turned away, and he who refuses it is invited, and he who did not accept the invitation disobeyed Allaah and His Messenger (salalahu alayhi wa sallam)." (Muslim) If you dont like it, leave it Yazid ibn al-Asamm (RA) reported: A newly-wedded man of Madinah invited us to a wedding feast, and he served us thirteen lizards. Some people ate it and some left it. (Muslim)