Ayatullah Sistani, may Allah (SWT) protect him, has “abstained” from issuing a fatwa on the subject of Tatbir (qama Zani) and Zanjeer Zani. Therefore, his muqallideen can refer to Fal 'Alam (next most learned Mujtahid) in this issue.
Who is the next most learned Marja?
The same method that you apply to identify the Marja Taqleed will be followed to find the Fal A'lam.
There are three ways of identifying Marja Taqleed:
1) When a person is certain that a particular person is a Mujtahid, or the most learned one. For this, he should be a learned person himself, and should possess the capacity to identify a Mujtahid or an A'alam;
2) When two persons, who are learned and just and possess the capacity to identify a Mujtahid or the A'alam, confirm that a person is a Mujtahid or an A'lam, provided that two other learned and just persons do not contradict them. In fact, being a Mujtahid or an A'lam can also be established by a statement of only one trusted and reliable person;
3) When a number of learned persons who possess the capacity to identify a Mujtahid or an A'lam, certify that a particular person is a Mujtahid or an A'lam, provided that one is satisfied by their statement.
https://www.sistani.org/english/qa/01191/
- By Fatema.Khimji