commentator
Your husband needs to file for his unemployment benefits. He will be asked to give a reason to the claims taker, and he will tell them he was let go at the 89th day of his probation. (He does not need a separation letter or anything else to file except the appropriate self identifications.) In order to be monetarily eligible he will need to have worked for covered employers enough during the last eighteen months to qualify.
The employer will be contacted. If they indicate it was for business related issues, or lack of need for his services, it will be an approved claim immediately. If they say it was poor performance, or misconduct of some type (such as absenteeism, theft, tardiness, violation of policy) then they will contact your husband, he will be given a chance to explain the circumstances and will be told what the company has said happened. A decision will be made at this point on whether he receives benefits, which is appealable by either party.
In any case, if you are thinking you can fight the termination on any grounds other than "fired for being a Presbyterian" which they are probably not going to say, (in other words EEOC issues,)you are mistaken. Unless EEOC comes into play, unemployment insurance is the only venue where you can protest or appeal this situation, and receiving benefits is the only recompense available even if the termination was totally unjust.