Hadith 88

Bulugh al-Maram

Book 8: Marriage

وَلِمُسْلِمٍ : { إِذَا دَعَا أَحَدُكُمْ أَخَاهُ , فَلْيُجِبْ; عُرْسًا كَانَ أَوْ نَحْوَهُ } 1‏ .‏

English

Muslims has:

"When one of you invites his brother, he must respond (i.e. attend), whether it is a wedding or something similar."