In VBRK table you can see field BELNR-Accounting Document Number and same field you can find in BSAD table also,
with this tables try to fetch the data. Orelse one step more forword you can also see the field XBLNR-Reference Document Number which is present in both VBRK and BSAD. And BUDAT-Posting Date in the Document is present in BSAD table.
Hope the above links will help you.
May be this statement can help you:-
SELECT bukrs lifnr augdt augbl zuonr belnr waers xblnr blart wrbtr sgtxt zlsch FROM bsak INTO CORRESPONDING FIELDS OF TABLE it_bsak WHERE blart IN s_blart AN budat IN s_budat AND AUGDT IN s_budat AND bukrs IN s_bukrs AND lifnr IN s_lifnr AND "it_ekko-lifnr or lifnr = s_lifnr ) and xblnr IN s_xblnr .