These additional financial sponsors also have to submit an Affidavit of Support, proof of their income, and proof of their legal status in the United States. A declaration is a simple statement that you intend in good faith to return to the United States to resume your domicile.View the sample form here. If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864). This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile.