The answer to your question, jessi, is that it depends.
The DOJ's National Criminal Justice Reference Service advises that an officer should never handcuff a suspect to a fixed object or to himself. However it is not illegal to do so.
The test as to whether a suspect's Fourth Amendment rights are violated by the handcuffing was outlined in Michigan v Summers, 452 US (1981). In addition, the Fourth Amendment, which gives a person the right to be free from "unreasonable seizure," had reasonableness defined in Graham v Connor, 490 US (1989).
Handcuffing is warranted when there is a risk of flight, when it is used to minimize the risk of harm to officers, and when done to facilitate the orderly completion of a search. The authority to detain incident to a search is unquestionned. It is the prolonged use beyond the time reasonably required under the circumstances that is a question.
Whether three hours handcuffed to a fixed object is unreasonable and a violation of your friend's Fourth Amendment rights depends on all of the facts.