Muhammad orders the torture of a man in order to get hold of a treasure

We learn of that in the earliest Muslim biography of Muhammad, pages 511-517 (758-766 in the Arabic).  The same pages also tell us that after the torture, Muhammad had the man beheaded.  Later that night, or the next, Muhammad took into his private tent for consummation of "marriage" the tortured man's widow, whose father and other male relatives, we read, Muhammad had just killed:
Kinana b. al-Rabi', who had the custody of the treasure of the B. al-Nadir, was brought to the apostle who asked him about it. He denied that he knew where it was. A Jew came (Tabari says "was brought") to the apostle and said that he had seen Kinana going round a certain ruin every morning early. When the apostle [Muhammad] said to Kinana, 'Do you know that if we find you have it I shall kill you?' he said Yes. The apostle gave orders that the ruin was to be excavated and some of the treasure was found. When he asked him about the rest he refused to produce it, so the apostle [Muhammad] gave orders to al-Zubayr b. al-'Awwam, 'Torture him until you extract what he has,' so he kindled a fire with flint and steel on his chest until he was nearly dead. Then the apostle delivered him to Muhammad b. Maslama and he struck off his head in revenge for his brother Mahmud. [-- page 515 (763-764 in the Arabic)]
...The apostle took captives...among whom was Safiya d. Huyayy b. Akhtab who had been the wife of Kinana b. al-Rabi’ b. Abu’l-Huqayq, and two cousins of hers. The apostle chose Safiya for himself. [-- page 511 (758 in the Arabic)]
When the apostle married Safiya in Khaybar or on the way, she having been beautified and combed, and got in a fit state for the apostle by Umm Sulaym d. Milhan mother of Anas b. Malik, the apostle passed the night with her in a tent of his. Abu Ayyub, Khalid b. Zayd brother of B. al-Najjar passed the night girt with his sword, guarding the apostle and going round the tent until in the morning the apostle saw him and asked him what he meant by his action. He replied, ‘I was afraid for you with this woman for you have killed her father, her husband, and her people, and till recently she was in unbelief, so I was afraid for you on her account.’ They allege that the apostle said ‘O God, preserve Abu Ayyub as he spent the night preserving me.’
[-- page 516-517 (766 in the Arabic)]