Much of the disagreement between schools of thought about mandates and prohibitions stems from interpreting a command in a religious text as a mandate (فرض) or a prohibition (تحريم) when it may only be a recommendation (ندب) or a discouragement (كراهة).
A good example is an event that happened during the life of the Prophet (PBUH). The two verses that are involved have been widely thought to be a case of one Quranic ruling that abrogated another. See this topic
for details. In 58:12, God commands Muslims who could afford it to offer a charity before seeking a private counsel with the Prophet (PBUH). What happened is that no one complied, except Ali! Why didn't they and why did he? Was it because they all understood that it was only a recommendation and Ali wanted to get its reward though he did not have to do it? Or was it because Ali was the only one who believed it was a mandate and everybody else got it wrong?
In 58:13, God acknowledges that most Muslims did not do as He ordered in the previous verse, and gives them a substitute order. Is that a modification of the prior order, as most scholars believe, and thus a case of abrogation, or is it simply a case of misunderstanding an order to be a mandate when it was actually only a recommendation?
Scholars of Foundations of Deduction (أصول الفقه) have formulated an excellent rule to enable them to discern a mandate from a recommendation and a prohibition from a discouragement. They specified two criteria, either of which will suffice:
- The text contains words that explicitly say whether the order is a mandate/prohibition versus recommendation/discouragement. Words like فريضة (a mandate), قضى (He decrees), كتب عليكم (It is written upon you), all clearly indicate a mandate. Words like حرمت عليكم (Prohibited to you), إنه كان فاحشة (It is a debauchery), فاجتنبوه (so, stay away from it) clearly indicate a prohibition. Words like خير لكم (is better for you), أزكى لكم (is more dignifying for you) clearly indicate a recommendation.
- In the absence of explicit words to confirm its mandatory nature, a command to do something is deemed a mandate if it is subsequently followed by a warning against not doing it. Without such warning, the first command is only a recommendation.
Despite this excellent rule, many scholars still ruled some orders a mandate when there was no clear indication that they were. By doing so, they made religious compliance stricter than perhaps they were meant to be.
It is clear to me that 58:13 was a recommendation, and that Muslims who did not follow it did so because they understood it as such. It is not clear though whether Ali shared that understanding, but I think he did.
A good example of the second criterion above is in this verse, prohibiting following anything other than what God has revealed,
In this verse, God orders us to follow what He revealed AND forbids us from following anything else. Both components make the order a mandate. Thus, when we are confronted with an issue where a mortal has ruled one way and the Quran has ruled differently, we have no choice but to favor the ruling of the Quran. That is why I see that the Sunna cannot abrogate verses of the Quran
as some have opined.