How to find files which contain specific string in directory using find

This is my directory structure.

dirOut
├── dirIn1
│   ├── temp1
│   └── temp2
├── dirIn2
└── dirIn3
    ├── temp1
    ├── temp2
    ├── temp3
    └── temp4

dir is directory and temp is file.
I want to find files which contain specific string "Hello".
How do I use command "find" to find.