Tachanun on Yartzeit of a parent

What is the source of the custom of not sayaing Tachanun on the Yartzeit of a Parent?

There is a chassidic custom not to say tachanun on the yortzeit of a Rebbe or holy man, since each year the soul attains a higher level in paradise, so it is a cause for celebration. Many authorities vigorously oppose this custom since we are not knowledgeable concerning what happens in higher worlds, and in our world the loss of a tzaddik is a cause of pain. I am not aquainted with a custom to carry over not saying tachanun to one's parent.