How to get href text which contains .xls or .xlsx text in an anchor tag using regex

How to get href text which contains .xls or .xlsx text in an anchor tag
using regex

Using regex I want to fetch an href which contains .xls or .xlsx text
I want to stick to this regex
<a\s*[^>]*\s*href\s*=\s*((?:[^ ]|[\n\r])+)\s*[^>]*>.*?<\/a>
But what should I add here so that I can get only the link which contains
.xls or .xlsx text in anchore tag.