transition provision

you''ll get credit  as per sec 140(3),  subject to condition mentioned in the sec 

(i) such inputs or goods are  used for making taxable
supplies under this Act;
(ii) the said registered person is eligible for input tax credit on such inputs under
this Act;
(iii) the said registered person is in possession of invoice or other prescribed
documents evidencing payment of duty under the existing law in respect of such
inputs;
(iv) such invoices or other prescribed documents were issued not earlier than
twelve months immediately preceding the appointed day; and
(v) the supplier of services is not eligible for any abatement under this Act:

which good/service you are dealing