“Mary and Abby!”/“Mary and Abby who?”/“Mary Christmas and a Abby New Year!”

An end-of-year knock-knock joke is:
 
“Knock, knock!”
“Who’s there?”
“Mary and Abby!”
“Mary and Abby who?”
“Mary Christmas and Abby New Year!”
     
The joke has been cited in print since at least 1994.
 
   
14 February 1994, The Daily News Leader (Staunton, VA), “Mighty FUnny’s Mini Jokes,” The Mini Page,  pg. 1, col. 1:     
Jake: Knock, knock.
Liz: Who’s there?
Jake: Mary and Abby.
Liz: Mary and Abby who?
Jake: Mary Christmas and Abby New Year!
(sent in by Mary Malcomb) 
 
Google Books
December 1994, Boys; Life, “Think & Grin,” pg. 73, col. 2:
Ted: Knock, knock.
Ed: Who’s there?
Ted: Mary and Abby.
Ed: Mary and Abby, who?
Ted: Mary Christmas and Abby New Year! — Matt Davidson, Duncanville, Tex.
 
15 December 1996, Newsday (Long Island, NY), “Jokes,” Kidsday sec., pg. 1: 
Knock, knock Who’s there? Mary and Abby Mary and Abby who? Mary Christmas and Abby New Year!—Jillian Cantor; Smithtown.
 
Twitter
Ileana Zirra‏
@Caleidoscop
Knock, knock!
Who’s there?
Mary and Abby!
Mary and Abby who?
Mary Christmas and Abby New Year!
10:45 AM - 8 Dec 2009
     
Google Books
Lots of Knock-Knock Jokes for Kids
By Whee Winn
Grand Rapids, MI: Zonderkidz
2016
Pg. ?:
Knock, knock.
Who’s there?
Mary and Abby.
Mary and Abby who?
Mary Christmas and Abby New Year!
 
Google Books
Christmas Jokes
By Delphon Coker
Xlibris Corporation (Xlibris.com)
2016
Pg. ?:
Santa had two friends Mary and Abby. What did he wish them during Yuletide season?
Answer: He wished them a Mary Christmas and a Abby New Year.
 
Reddit—Dad Jokes
Knock Knock! (self.dadjokes)
submitted December 27, 2017 by Flying_Dutchmen_13
Whos there? Mary and Abby! Mary and Abby who? Mary christmas and a Abby new year.
 
Twitter
Dad Jokes‏
@Dadsaysjokes
1) Knock knock!
2) Who’s there?
1) Mary and Abby!
2) Mary and Abby who?
1) Mary Christmas and a Abby new year.
9:05 PM - 27 Dec 2017