Note: while the use-case described is about using submodules within a project, the same applies to a normal git clone
of a repository over HTTP.
I have
For Windows
Goto --> C:/Users/user_name/gitconfig
Update gitconfig file with below details
[http]
[https]
proxy = https://your_proxy:your_port
[http]
proxy = http://your_proxy:your_port
How to check your proxy and port number?
Internet Explorer -> Settings -> Internet Options -> Connections -> LAN Settings