Have a look here you could do something like this ....
declare
@dbPrefix varchar(2),
@cob varchar(20) ,
@m_cobMinusOne datetime,
@m_cobEOM varchar(20),
@SqlQuery NVARCHAR(MAX);
set @cob = '20131211';
set @dbPrefix = 'q_';
set @m_cobMinusOne = convert(varchar(20),@m_cobMinusOne,103);
set @m_cobEOM = convert(varchar(20),@m_cobMinusOne,103);
SET @SqlQuery = N'select @m_cobMinusOne = bdh_prev_bus_d , @m_cobEOM = bdh_prev_mo_end_d ' +
N'from ' + QUOTENAME(@dbPrefix+'dbbdm005') +'..bdh_bus_date_ref ' +
N'where bdh_bus_d = @cob';
EXECUTE sp_executesql @SqlQuery
,N'@m_cobMinusOne VARCHAR(20) OUTPUT, @m_cobEOM VARCHAR(20) OUTPUT, @cob VARCHAR(20)'
,@m_cobMinusOne OUTPUT
,@m_cobEOM OUTPUT
,@cob