One thing that is important is that Allah does not accept or forgive kufr, while He may forgive a sin. As such, the fuqaha tell us that agreeing to let someone remain a kafir could be kufr! (e.g. if someone asks you to give them the shahada, or how to become Muslim, and you refuse.) As such, in such situations, we let the person become Muslim. And explain to him that obligation to fast, and then explain the spiritual significance of the action. Like Sayyidi Ibn `Ata'illah said in his Hikam, "Actions are lifeless forms whose soul is the secret of sincerity in them." If we present the duties and obligations of Islam as "chores", then people would be reluctant to do them. But if we go through the door of love, spiritual significance, and the "joy of slavehood to Allah" because of the meaning, purpose, significance and direction it gives one's life, then few who had the will to convert would refuse. Also, we should present such obligations, to new converts, in a way that does not make it seem that the validity of their being a Muslim rests on the performance of these duties. They must be Muslim. Salvifically, they don't have a choice. But (while accepting that they are obligatory) the non-performance of religious duties is sinful, but does not prevent ultimate salvation. (Even though it could well result in punishment.) Once, in the early 90s, some of us upset of Shaykh Abdullah Hakim Quick, when he was still in Toronto, and was one of my first mentors in deen. I sister wanted to convert right at the beginning of Ramadan, but her (staunchly Christian) mother was with her, and it was impossible for her to fast if she converted. We didn't know what to do, so we asked Shaykh Abdullah Hakim Quick. He told us, firmly, that we should tell her to become Muslim. If she doesn't fast, but is a Muslim, it is better than for her to remain an unbeliever. She entered Islam. Within a few days, in the company of other believers, she started fasting.
This follows the ruling of commanding the good and forbidding the wrong. The essential purpose of commanding the good and forbidding the evil this is to increase the good, and reduce wrong. As such, it must be done after clear thinking and proper assessment of the situation, and possible outcomes. Until reasonably sure that one's words or actions will be of benefit (the least of which would be to affirm the truth, even if it is not heeded), and bereft of harm, one should not act. The scholars deduce this from the Prophet's words (Allah bless him and give him peace), "Whoever believes in Allah and the Last Day, let him say what is good or remain silent." [Bukhari and Muslim]
Imam Nawawi (Allah have mercy on him) said,
"Every legally responsible person should refrain from saying anything except when there is a clear advantage to speaking. Whenever speaking and not speaking are of equal benefit, it is sunna to remain silent, for permissible speech easily leads to that which is unlawful or offensive, as actually happens much or even most of the time - and there is no substitute for safety. The Prophet (Allah) bless him and give him peace) said, "Whoever believes in Allah and the Last Day, let him say what is good or remain silent."
This hadith, whose authenticity Bukhari and Muslim concur upon, is an explicit legal text indicating that a person should not speak unless what he intends to say is good, meaning that the benefit of it is apparent to him. Whenever one doubts that there is a clear advantage, one should not speak. Imam Shafi`i (Allah have mercy on him) said, "When one wishes to speak, one must first reflect, and if there is a clear interest to be served by speaking, one speaks, while if one doubts it, one remains silent until the advantage becomes apparent." [Nawawi, al-Adhkar, as translated by Shaykh Nuh Keller, Reliance of the Traveller, r.1.1]
The Essentials Of The Fiqh Of Commanding The Good And Forbidding The Evil
1. Commanding the good and forbidding the evil is one of the most important of Islamic duties. The Prophet (Allah bless him & give him peace) cautioned us, "Command the right and forbid the wrong, or Allah will put the worst of you in charge of the best of you, and the best will supplicate Allah and be left unanswered."
2. Scholars mention, however, that commanding the good and forbidding the evil is only obligatory if one thinks that the person would listen.
3. Otherwise, if one does not think they will listen, it is recommended.
4. However, if a greater harm or worsening of the situation is feared, then it would be better (or even obligatory, in some cases) not to say anything, because legally one choose the less harmful of two matters.
5. It would be an obligation, however, to hate the wrong in one's heart.
6. With this, if it is ongoing in one's presence (such as listening to unlawful talk) it would be obligatory to leave if even stopping it (such as by subtly changing the topic) is not possible. Similarly, if a sister is not properly covered, one cannot allow oneself to look at her uncovered hair or limbs. Similarly, if a brother is wearing very tight trousers, one cannot look at the (tightly-covered) area between his navel and knees.
7. Sayyidi Abd al-Ghani al-Nabulsi (Allah have mercy on him) cautions that the general Prophetic way in commanding the good and forbidding the evil is to do so in a discreet, non-specific manner, in order to preserve the honor and feelings of the one who is wrongdoing to the extent possible.
[From: Sharh al-Tariqa al-Muhammadiyya, Sayyidi Abd al-Ghani al- Nabulsi; Radd al-Muhtar, Allama Ibn Abidin; al-Hadhr wa'l Ibaha, Shaykh Khalil al-Nahlawi]Walaikum assalam, Faraz Rabbani