If I were to swear by Allah nine times that, indeed, the Messenger of Allah ﷺ has been killed, that would be more beloved to me than swearing only once, because Allah the Exalted took His Prophet and made him into a martyr.
لَأَنْ أَحْلِفَ بِاللهِ تِسْعًا إِنَّ رَسُولَ اللهِ ﷺ قُتِلَ قَتْلًا أَحَبُّ إِلَيَّ مِنْ أَنْ أَحْلِفَ وَاحِدَةً وَذَلِكَ بِأَنَّ اللهَ ﷻ اتَّخَذَهُ نَبِيًّا وَجَعَلَهُ شَهِيدًا