Does a mohel say Tachanun during mincha if he did a brit in the morning?

In a shul where a mohel is present for a brit, he (nor others in the minyan) say Tachanun. Usually, a brit is done after Shacharit.

Someone (not a mohel) told me, recently, that when a mohel has doen a brit in the morning, he is exempt from saying Tachanun during mincha, regardless of which shul he attends (i.e., even if not doing a brit at mincha.) I haven't been able to locate a source to support this. Is this halacha or a minhag?

Answer

I have heard this as well, because it is considered a Yom Tov for the Baalei Habris (the father and Sandik are also exempt, IIRC). This halacha is brought here from the Halacha Berura, although I believe it has earlier sources as well.

Edit: The concept of it being a Yom Tov for the Baalei Habris can be found in the Rema OC 135:1, and there are a number of other early sources as well.