Hi Madhuri
generally if you want to Make it mandatory go vov8 .. Select your document type And give Ref Mandatory.
but in case it is not mandatory To give reference , Go to copy control VTAA
3 Setting needed
1) You maintain Update Document --- X
2) In positive and negative Field maintain +
3) And finally go to OVZ9 T.code consignment checking rule is AW Availability check is 02
go inside and Dont activate the check box " Include sales req ''
So now you can achieve this ,please update here after the results
If i am wrong please comment on this
Thanks a lot