Query the contents of stored procedures on SQL Server

I am exploring a legacy database system and have very little knowledge of its internals. I would like to find all the stored procedures that invoke another stored procedure A.

How best to do this?

Can I write something like this pseudocode:

select name from AllStoredProcedures as Asp where Asp.TextualContent contains 'A'

Asp.TextualContent means the actual SQL contained in the SP.