Reflog

λ git log --oneline d889863 Flexbox 1st commit a70a8d1 GitBook API Example sdfdsd3 GitBook API Example2 sdfdsg2 GitBook API Example3

λ> git reflog
d889863 HEAD@{0}: commit: Flexbox 1st commit
a70a8d1 HEAD@{1}: clone: from https://git.gitbook.com/hemantajax/css-flexbox.git
sdfdsd3 HEAD@{2}: commit: 2nd commit
sdfdsg2 HEAD@{3}: commit: 1st commit

if you do git reset --hard a70a8d1 then you have only one commit in your history

git log --online
a70a8d1 HEAD@{3}: commit: 1st commit

What if you want to take your history ( other 3 commit back )

git reflog HEAD@{0}
// now detached state
// merge to master
git checkout -b my-branch
git checkout master
git merge my-branch