Gertrude Stein Quotation

Gertrude Stein once wrote, “What a day was today. What a day was the day before yesterday.”
Where did she write this; in what work, that is.
And I think it is about a standard expression, What a day was today! and she thinks one may as well say what a day was the day before yesterday or any day or both. Like with any cliche or proverb or old saying or fixed expression: one may as well sayanything else. But does her quotation mean something else? I looked on all the 200,000 sites that claim to be about Gertrude Stein, so don’t bother to look there. They all lead to the same place or two that just list a few famous sayings of hers butnot this one, or they lead to claims of telling you where the quotation is but are just encyclopaedias that also don’t have that one in them, or they emphasize how she was a feminist, etc.