All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Celebrating an anniversary for the occasion of marriage is not among the customs or religious rites of Muslims. Indeed it is a custom of Christians and other non-Muslims, and the Prophet forbade us from imitating them as he said: "He is not one of us, he who imitates non-Muslims, so do not imitate the Jews and the Christians." [At-Tirmithi] The Prophet also said: "Be different from non-Muslims." [Al-Bukhari and Muslim] Another narration reads: "Whoever imitates a people he is one of them." [Abu Daawood] Therefore, we do not consider this celebration permissible. Rather, a Muslim should avoid imitating non-Muslims and following their path, so that he will not fall under the category of people that are mentioned in the narration of the Prophet "Whoever imitates a people he is one of them." Thus, it is forbidden to celebrate this occasion even if it is only between the two spouses.
Allaah Knows best.