SarahJane, from memory here, so forgive me if I'm wrong...

I do believe it was Abraham and Sarah (or Abram and Sarai ??). It was Sarah that didn't believe the promise God gave to them and asked Abraham to sleep with the servant (whose name completely escapes me). Ishmael was born of that union, and I'm told that's where the Islamic faith sprang from.

Eventually God fulfilled the promise to Sarah and Abraham and Sarah gave birth to Isaac. The Jewish, and eventually Christian, faith came from that line.

Again, this is from memory, and I have to go out soon so I don't have time to look things up and confirm that I'm correct - but this is what I recall and have been taught in Church. I'm sorry if I've goofed in some way.

BW