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saburinasanhashyokudoudenuidasoudesu. "(According to what I was told), Sabrina undressed in the dining-room."
saburinasanniyorutomahoutsukaisamagatata,tasoudesu. "According to Sabrina, the wizard cast a spell." That's her story, anyway.
mahoutsukaisamaniyorutosaburinasangatotemourusaka,tasoudesu. "According to the wizard, Sabrina was very noisy."
This construction specifically implies that the speaker is passing on information obtained from someone else and not checked.
As mentioned in Appearances and Deductions, this construction is confusingly similar to, but slightly different from, the soudesu which indicates appearance or deduction.
The connectivity is that soudesu follows the plain form:
The source of the information (if specified) is followed by niyoruto. Two alternatives, niyoreba and deha, seem to be identical in implication to niyoruto.
tomodachiha(saburinasanhashyokudoudenuida)toiimashita. "A friend said 'Sabrina undressed in the dining room'".
tomodachihasaburinasangashyokudoudenuidatoiimashita. "A friend said Sabrina undressed in the dining room".
The patterns for direct quotes (A) toiimasu and indirect quotes A tooimasu are near enough identical, since brackets aren't audible. They only become different when first/second/third person or location has to change. iimasu is the polite form of iu, "to say" or "to tell".
saburinasanha(watashihaodoritakunaidesu)toiimashita. "Sabrina said 'I don't want to dance'".
saburinasanhaodoritagaranaka,tatoiimashita. "Sabrina said she didn't want to dance." Note the insertion of garu since this is now a third-person want.
tomodachiha(mahoutsukaisamahashyokudounikitatokorodesu)toiimashita. "A friend said 'The wizard had just come to the dining-room'."
tomodachihamahoutsukaisamahashyokudounii,tatokorodesutoiimashita. "A friend said the wizard had just gone to the dining-room."
These two sentences describe the same report of the same action. The friend was in the dining-room when the wizard entered, but is now somewhere else gossipping about what happened there, so kuru changes to iku.