Had to look it up but apparently rexx was first released in 1979. My first thought for a contender was the Bourne shell for unix but it too was released in 1979. The earlier Thompson shell(1971) apparently was not really designed for scripting. csh was released with 2bsd in 1978.

But then I got off the unix kick and looked at the xerox alto which had a smalltalk environment and smalltalk was first released in 1972 and I would say that due to it's interactive nature smalltalk is defiantly a scripting language.

But then I looked at lisp, and it is hard to say if lisp is a scripting language, it could have been, however it was invented and implemented before there were really environments to script. but I am still going to give the award to lisp. and from the wikipedia page, I thought this was pretty great.

    "According to McCarthy

    Steve Russell said, look, why don't I program this eval ...
    and I said to him, ho, ho, you're confusing theory with practice, 
    this eval is intended for reading, not for computing. 
    But he went ahead and did it. 
    That is, he compiled the eval in my paper into IBM 704 machine code, 
    fixing bugs, and then advertised this as a Lisp interpreter, which it certainly was.
    So at that point Lisp had essentially the form that it has today ...
    "