http://samueleresca.net/2014/12/ssrs-return-stored-procedure-dependencies/

SSRSreturnSPDep.sql

-- =============================================
-- Author:Resca Samuele
-- Description: Returns names of stored procedure that are used in report
-- =============================================
CREATE PROCEDURE [dbo].[ReportSPROCDependencies]
@ReportName nvarchar(MAX) = NULL
AS
BEGIN
SET NOCOUNT ON;

;WITH XMLNAMESPACES (
DEFAULT
--IMPORTANT(!) There are different namespaces for every version of Sql server.
'http://schemas.microsoft.com/sqlserver/reporting/2010/01/reportdefinition',
'http://schemas.microsoft.com/SQLServer/reporting/reportdesigner' AS rd
)
SELECT DISTINCT
Name,
Path,
xmldoc.VALUE('CommandType[1]', 'VARCHAR(50)') AS CommandType,
xmldoc.VALUE('CommandText[1]','VARCHAR(100)') AS StoredProcedreName
FROM (
        SELECT name, path,
        CAST(CAST(content AS VARBINARY(MAX)) AS XML) AS reportXML
        FROM ReportServer.dbo.Catalog
) tmp
CROSS APPLY reportXML.nodes('/Report/DataSets/DataSet/Query') r(xmldoc)
WHERE xmldoc.VALUE('CommandType[1]', 'VARCHAR(50)') = 'StoredProcedure'
AND (@ReportName LIKE '%'+@ReportName+'%' OR @ReportName IS NULL)
END