Somehow I've managed to turn off the switch that causes irritation with my husband, and also, in general. The irritation is not helpful for me or for him. I don't want him to feel bad about his Alzheimer's Disease. I just do not let myself react. As @jbur said, "pause". Put it in the context, he's asking me this again because of the disease. He's not asking me the same question over and over again just to irritate me.
I also try to engage him as much as possible. When he asks me what day it is, I reply, "Yesterday was Saturday, and tomorrow will be Monday." He still knows the answer.
Part of my philosophy of caregiving is creating a safe environment for my husband so he's comfortable, shares his feelings, and feels free to ask me anything. I think of myself as his guide.