Travel Expense Report: Validation to be placed on SAVE & SEND FOR APPROVAL

Hi All,

I have come up with requirement in Travel Expense report creation.

As you all know after filling expense report we have two options available

1 SAVE

2 SAVE & SEND FOR APPROVAL

I need to put few validation when user is clicks on "SAVE & SEND FOR APPROVAL" .

Please let me know how can it be achieved.