There are plenty of references available on permissibility of celebrating Mawlid. In fact majority of muslim scholars (IJMA) agreed on this.

In Haramayn (i.e. Makkah and Madina), in Egypt, Yemen rather all people of Arab world have been celebrating Mawlid for long. Upon sight of the moon in Rabi ul Awwal their happiness touches the limits and hence they make specific gatherings for Dhikr of Mawlid due to which they earn immense Ajr and Success.[Biyan al Milaad an Nabwi, Page No. 58]

may allah protect us from evil..