If the item was never yours to begin with and it belongs to your husband then you shouldn't really have listed it for sale. You can't list another person's item for sale without their consent and then be surprised when they object to you selling it!
If your husband originally agreed to you advertising the item for sale but subsequently changed his mind after the buyer purchased it then I suppose you could just turn around and say "Tough luck - I've already sold it, so it's going", although it may well result in some bad feeling between the two of you if you were to stick to your guns and do that.
If the item in question has some kind of sentimental value to your husband and you don't want to risk falling out with him over the matter then I would advise you to contact the buyer, explain what has happened and say that as a result you will now not be selling the item, making sure that you apologise to the buyer for any inconvenience and disappointment caused. If you do decide to take this course of action then the buyer is likely to be cheesed off by the fact that you reneged on the sale, so you would have to be prepared to take the risk of the buyer leaving negative feedback in relation to the transaction and taking the hit on your account in the form of a selling defect.
If there are any further goods that you are clearing out but have not yet listed then go through them all with your husband, putting aside all of the items he wishes to keep and listing for sale those items he doesn't mind getting rid of. If there are only a handful of items that he wishes to keep then it may not even prove to be problematic; however, if he is something of a hoarder and wants to keep more items than he is willing to allow you to list for sale then you may well have to have a serious talk with him about where to draw the line between how many items you are actually willing to hang onto!
