Obligations are According to Ability
On the authority of Abu Hurayrah (may Allah be pleased with him) who said: I heard the Messenger of Allah (peace be upon him) say:
What I have forbidden for you, avoid. What I have ordered you [to do], do as much of it as you can. For verily, it was only their excessive questioning and disagreeing with their Prophets that destroyed [the nations] who were before you.
[Al-Bukhari & Muslim]
عن أبي هريرة عبدالرحمن بن صخر رضي الله عنه، قال:
سمعت رسول الله يقول: ما نهيتكم عنه فاجتنبوه، وما أمرتكم به فأتوا منه ما استطعتم، فإنما أهلك الذين من قبلكم كثرة مسائلهم واختلافهم على أنبيائهم.
رواه البخاري:7288، ومسلم:1337.
Written commentary compiled by volunteers utilizing Sh. Jamaal Diwan's audio commentary above and English translation of Ibn Daqiq Al-Id's commentary on The Forty Hadith of Imam al-Nawawi.
There is another narration for this hadith that gives a deeper understanding of its meaning:
The Messenger of Allah (sas) addressed us and said,
O people! Hajj has been made obligatory upon you, so perform the Hajj. A man asked, "Is that every year, O Messenger of Allah?" The Prophet (sas) remained silent while the man repeated his question three times. Then he said, "If I had said 'yes' then it would have become obligatory upon you [i.e. every year], and you would not have been able to do so. Do not ask me about that which I have left unspecified, for verily the nations before you were destroyed by their excessive questioning and argumentation with their Prophets. If I order you with something then do as much of it as you are able, and if I forbid you from something then keep away from it."
In both of these narrations, the prophet (sas) commands us to avoid what he has forbidden and to follow what he has ordered us to do according to the best of our ability.
The Prophet (sas) also asks us to follow his guidance without asking too many questions, and to pay attention to the types of questions we ask.
Stay Away from What is Prohibited
"What I have forbidden for you, avoid.” We have to follow this command all the time, and in all situations. This order has to be followed except under dire circumstances, such as when one is starving and there is no food available except for some meat that was not properly slaughtered. In conditions other than that of necessity, however, all Muslims have to avoid what is forbidden.
Obligations are According to Ability
"What I have ordered you to do, do as much of it as you can" is an important principle of Islam. The Prophet (sas) is indicating that we won’t be able to do all what is required, but we have to do as much of it as we can. Based upon this principle are countless other rulings. Prayer, for example: the Prophet (sas) said, 'Pray standing; if you are not able to; pray sitting, if you are not able to; pray (while lying) on your side."
The scholars have differed over the meaning of a command by the Prophet to perform an action - does it imply repetition? That is, if we are ordered to do something then does that automatically imply that we must do it repeatedly? Or does it mean that doing it once is sufficient unless otherwise specified? For example, we are commanded with Hajj once in a lifetime, but we are also commanded with Salah five times every day. Most of the scholars decided that a command does not automatically imply repetition, while others said that we should rule on whether it implies repetition or not without further evidence.
Asking Too Many Questions
Asking too many questions can be a problem in itself, particularly if we are talking about the kinds of questions that are excessive or that can clearly lead to something that you don’t want to know an answer to. We also shouldn’t ask questions that are accompanied with a degree of arrogance or are just a waste of time.
The companions of the Prophet (sas) rarely asked questions. In fact, there were only thirteen questions that were answered in the Quran. The answers to their few, numbered questions are in verses such as: “They ask you about the moon cycles,” “They ask you about menstruation,” “They ask you about the bounties of war.” Anas said, “We were prohibited to ask the Prophet (sas) too many questions. So we would be very happy when an intelligent bedouin came to the Prophet and asked him questions, so we could listen.” Asking too many questions and disagreeing with the Messenger (sas) can cause our destruction. If it happened to the people before us, it can happen to us too.
What Takes Precedence: Doing Obligatory Actions or Staying Away from What is Prohibited
According to scholars, avoiding bad deeds takes precedence over doing good deeds when the bad deed is clearly prohibited and the good deed is a recommended act. When the good deed is obligatory, doing it is greater because it involves acting upon something that Allah wants from you. It is proactive obedience, as opposed to a somewhat passive avoidance of what is forbidden (although to say leaving the haram is passive is a bit of a generalization). This is an interesting discussion and some scholars will argue different perspectives.