From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer rules that a son is not only permitted but obligated to direct all of his ma'aser and tzedakah funds exclusively to his parents until their needs are met, before distributing to any other poor person. The general prohibition against giving all charitable gifts to a single pauper does not apply when that recipient is one's own father or mother. The Usha enactment limiting charitable giving to one-fifth also does not apply to the obligation of kibud av va'em.
Source: Shu"t Chasam Sofer YD §229