Quoted from shia blog, with edition:

Shaykh of shias, Shahid Thani said, as it is in “al Diraya” (p 27):

إن جماعة كثير أجازوا العمل بالخبر الضعيف إذا إعتضد بشهرة الفتوى بمضمونه في كتب الفقه ، بتعليل إن ذلك يوجب قوة الظن بصدق الرواية وان ضعف الطريق ،فإن الطريق الضعيف قد يثبت به الخبر مع اشتهار مضمونه

“Indeed a large group of scholars permitted acting by da’eef hadith when appealed by popularity of fatwas (religious rulings) by its content in the books of Islamic jurisprudence, because it strengthens belief on the hadith being true despite its weak chain of narration. Therefore if the chain of narration is weak, the hadith is still established due to its popular content.”

As it also quoted by Muhyidin al-Musawi in “Qawaid al-Hadith” (p 109)