Answer
(Fatwa: 98/79/N=1434)
If Sahih or Hasan hadith is available then no Imam accepts week hadith in any case. But if no Sahih or Hasan hadith is available or it is not clear on the ruling then in proving the ruling or fixing a meaning the week hadith is accepted by all the Imams and it is given preference on Qiyas, not only Ahnaf. For details see the booklet “Hadith Zaeef Ki Istidlali Haysiyat” by Hadhrat Mufti Abdullah Maroofi, Ustad Takhassus Fil Hadith, Darul Uloom Deoband. This booklet is available on the website of Darul Uloom as well.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband