The beard of imam is less than one fist in my mosques so I want to pray salah in his back or shall I pray salah myself alone because one mufti told that if we pray salah behind such imam whose beard is less, then the fardh of salah shall be done but it is makrooh tahrimi and again you should repeat that salah. What should I do?

Answered according to Hanafi Fiqh by

بسم الله الرحمن الرحيم

(Fatwa: 666/664/N=06/1435)

If there is a mosque nearby where the imam follows the Shariah completely then you should offer salah behind him. And if there is no other mosque nearby or the imam there too is not complying Shariah then instead of offering salah alone you should offer salah behind such imam. Hence in this case you should only offer salah with jamah and not offer alone.
قال فى الدر (مع الرد كتاب الصلاة، باب الإمامة 2:301 ط مكتبة زكريا ديوبند): وفى النهر عن المحيط: صلى خلف فاسق أو مبتدع نال فضل الجماعة اهـ فى الرد: قوله: “نال فضل الجماعة” أفاد أن الصلاة خلفهما أولى من الانفراد لكن لا ينال كما ينال خلف تقي ورع … اهـ

Allah knows Best!

Darul Ifta,
Darul Uloom Deoband