SQL Server: Execute dynamic SQL command with Where clause inside Stored Procedure

hi

I have code like below but doesn't work when if put where clause in  set @ts

set @ts = 'select '+ @xhr +' from tblTotAbsen where no_induk ='+ @no_induk

but without clause where coding is work 

set @ts = 'select '+ @xhr +' from tblTotAbsen 

problem how this code below work if using where clause

ALTER PROCEDURE [dbo].[BacaRumus]
    @no_induk nvarchar(50)
AS
    BEGIN
    SET NOCOUNT ON;
    declare @xhr nvarchar(max),@ts nvarchar(max)
    set @xhr = 'no_induk,xmasukp,xoff,xmasukp + xoff as totsw'
    set @ts = 'select '+ @xhr +' from tblTotAbsen where no_induk ='+ @no_induk
    Exec (@ts)
END

thanks