yes a war did stop at christmas,  December 25th 1914. german soldiers started to sing "Stille Nacht, Heilige Nacht" (silent night to you and me). recognizing the tune, english soldiers joined in, presents of tobacco and chocolate and handshakes were exchanged and several games of soccer were enjoyed ( i expect the brits lost on penalties). Hostilities resumed at 8-30 am on the 26th. Evidence has been found and observations made that the truce was observed every christmas of ww1.