Ex-Tenant wants me to sign Affidavit. Whats that about ?

[Maugno M.]

I had a tenant that rented from me for almost a year. (December 2017 - November 2018) He has been asking for for a couple months now if i could write a letter stating that he lived there for that period of time. He says he is going through immigration and is trying to get his legal documents. 
I told him that i could not do that and that his lease and receipts were all the proof he needed from me but he states he never really saved those papers. He calls me this morning again, and says a lawyer already filled up paper and i just need to sign.
I asked him to send me a picture of the paper, and it is an affidavit stating that he lived in one of my mobile homes. The affidavit just says he lived there for that period of time and i need to sign at bottom.

Should i? Any liability on my part ?  I'm afraid they trying to sue me or something and they didn't have any paperwork so now here i go signing an affidavit. 
If it really is for his immigration status, maybe he just needs proof that he has been here in the U.S. Thoughts ?