Hi,
as a Schalke supporter I feel urged to reply to this. Most of the problems in this case have come up because of misunderstandings (and misinterpretations by some) that I would like to clarify here:
1. This isnt a normal chant, this is our anthem. It was created in 1924, but the current lyrics including the discussed stanza were added in 1963. Most of them (again including this stanza) were taking from a 1797 hunting poem called "Green oh Green" in which one argument for the colour is that the prophet chose it (which is correct if I am not completley mistaken).
2. The Ruhr area and especially Schalke has been a melting pot of cultures and religions for decades now. Especially in the 60s, when the area provided a lot of jobs due to its heavy coal mining and steel industry, thousands of people came in, especially from Turkey and Poland.
Football has always been a major part in the lives of people in the area and so the clubs, especially Schalke, Dortmund and Essen became meeting points for all the people working in coal mines during the week. Schalke in particular became known for its integration policies (the club got big thanks to polish players in the 20s). We were a very successful club in the 30s which caused the Nazis to use Schalke as propaganda and sadly some people in the club cooperated, but after the end of the war the club regained its attitude.
Now when the anthem was rewritten in the 1963, there was not much knowledge about islam despite the fact that a lot of muslims were just coming in. We have always been and are still a club that is mostly relying on heart/friendship/open-mindedness between all members, though sometimes not really exactly caring for mere facts, and so the writer decided to just quote the old lyrics and reword them to the current anthem.
This was supposed to be (and seen as by the muslims!) as a welcome gesture to the family of Schalke in which neither color nor religion nor background matters.
If anyone is a Schalker, he is my brother.
We know now that the colors blue and white dont really have a connection with the prophet, but it is part of our tradition and so we still sing it before every game, underlining the importance of that feeling around Schalke, that everyone is welcome here (unless a dortmund supporter, but thats a different story

).
3. As I said, there are many muslim fans (and even players such as currently Halil Altintop) at Schalke - none of them took offense in the past decades, in fact, they were thankful and proud to have the prophet mentioned as such (we have a pretty relaxed attitude towards all religions at the club.... Pope John Paul was here once and before he cud say no he was handed a membership so we can call him a member of the club too. And once there was a church campaign stating "No one gets past Jesus" - one of our supporters wrote "except Stan Libuda" (one of our greatest wingers) below it).
4. Due to a lot of emails that the club has received in the last couple days, Schalke has hired an expert on Islam to check the background and whether the wording is offensive - he basically said what I have said above and said that despite the wording that may cause some irritation, this is a very helpful song and the glass should be seen half full here. We also contacted the German Islamic Council who said the same.
The reason I write all this is that I have been hearing that all this background isnt really coming across in some media (even German media are writing wrong facts) - and in Germany the image of muslims suffers when emails come in stating "dont be surprised if a bomb goes off in the stadium", "Take it out or carry the consequences" etc. I know these are just a few extremists but unfortunately those are the ones that make the media sell stories and like everywhere in the world there are people who are easily convinced/mislead by such news.
The club stated today that there will be even more dialogue in the future, but after consideration by and discussion with a lot of muslims it was decided that the anthem remains unchanged.
I hope I could explain the background of the lyrics a little bit and I ask you to maybe point them out to friends if you ever discuss this (although really I have to say that I think the world has bigger problems than a song of a football club).
Thanks a lot to everyone who made it through everything,
greetings from Germany!