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 git@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.