ABBA with Rudi Carell at Am Laufenden Band on German tv in February 1978.
The host is making jokes with the ABBA members by mixing the two couples up. Agnetha: Das ist nicht richtig (This is not correct) and by asking Frida how her new baby is doing. Frida: Das ist nicht mein Sohn (It is not my son).
Agnetha then says that her son already talks and says: abba abba abba!