Is it true that all rulings of the Hanafi school of thought are supported by evidence from the Quran or Sunnah, and if not, can examples be given of rulings that have no evidence or whose evidence is based on a weak hadith?

The gist of the Fatwa:

Reputable jurists issue fatwas only based on legitimate Sharia evidence. Jurisprudential differences have multiple causes, including: a jurist not believing in the authenticity of a specific hadith, the hadith not reaching them, or their belief that the ruling has been abrogated. Examples of some jurists, such as the Hanafis, relying on weak hadiths include: their saying that ablution is invalidated by loud laughter during prayer, and their saying that usury is permissible between a Muslim and a non-Muslim combatant in a land of war. This is based on hadiths they believed to be authentic.