"Birthday"by Marc  Chagall. Here is a link to the painting from the provenance department at MoMA:  http://www.moma.org/collection/provenance/provenance_object.php?object_id=79360
My father also had Chagall's "Over Vitebsk" which is now also in the Museum: http://www.moma.org/collection/provenance/provenance_object.php?object_id=79370