There are multiple ways to find files containing a text string. Here is one simple command (grep) to achieve the goal.

grep -ril "texthere" directory

find command is also recommend because of speed and ability to deal with filenames that contain spaces.
find . -type f -exec grep -l "foo" {} +

Older UNIX version can use xargs to speed up the search:
find /path/to/dir -type f | xargs grep -l "foo"