Here is the problem, you need to merge some works from "stable" branch in "repo1" to your current "master" branch. Below are the steps you do.
First of all, add a remote repository
git remote add foo email@example.com:foo/repo1.git
then download objects and refs from that newly added remote repository
git fetch foo
now checkout the branch which will you merge, in this case "stable"
git checkout --track -b stable foo/stable
then you move back to your current directory
git checkout master
from this point, you can merge "stable" branch to your current "master" branch by using
git merge stable
if the changes don't conflict, you're done. Alternatively, you can pick out individual commits from "repo1/stable" to your current branch by using
git cherry-pick refnumber
Got better solutions? Please share it on the comments.