Unfortunately, there is no evidence to proof it being Halal. However, I will go through the main reason of why some scholars mark it Haram with explanation on why they it is wrong:

The first major Sahih Hadith that the scholars usually refer to is:

> ومن تشبه بقوم فهو منهم

> Whomever acts like some people then he is from them.

To repute this reason, if you claim that birthdays are Haram because of such hadith, then I can think of thousands of things that we took from non Muslims and use/understand from them. Many fields including theology, science, medicine, etc. The prophet PBUH never reputed taking something from other religions or societies simply because they were non Muslims.

Additional proof that it is OK is the growing number of scholars that are allowing celebration of similar days like memorial day/national day.

I would also advise you of doing a search on existing questions that were asked thoroughly from both sides:

http://islam.stackexchange.com/search?q=birthday