The following is from the english translation of the Arabic book 'The Khilafah' which is an extract from the book The Islamic Personality (Shaksiyyah Islamiyyah), Volume 2 by Sheikh Taqiuddin an-Nabhani (rh):
To refrain from establishing a Khaleefah for the Muslims is a great sin because it is abstaining from carrying out a very important fard of Islam, upon which the implementation of the divine laws depends, even upon which the presence of Islam in the battlefield of life depends as well. So Muslims as a whole commit a great sin by refraining from establishing a Khaleefah for all Muslims. And if they agreed to remain without a Khaleefah the sin would befall all Muslims in the entire world. If some of the Muslims embarked on working to establish a Khaleefah and the others did not, the sin will drop from the shoulders of those who started to work to establish the Khaleefah, while the fard remains on them until the Khaleefah is appointed. This is so because the involvement in establishing the fard removes the sin for the delay of its fulfilment in its time, and for its non-fulfilment despite one’s engagement in the work for establishing it, and despite his hatred of that which prevents him from accomplishing it.
As for those who were not engaged in the work for establishing the fard, the sin will remain on them as soon as the three days period has passed, from the departure of the Khaleefah until the appointment of a new Khaleefah, because Allah (swt) has entrusted them with a fard, which they did not carry out nor engage themselves in the work which is required for its completion. Therefore, they are sinful and deserve the punishment and shame from Allah (swt) in this life and the hereafter. They are sinful due to their refrain from establishing the Khaleefah or from the actions which (according to Shari‘ah) establish the Khaleefah. It is clear and obvious that a Muslim deserves the punishment of Allah (swt) when he ignores any of the duties enjoined upon him, particularly the duty by which the other duties are implemented and the Shari‘ah rules are established and the matter of Islam is brought aloft and the word of Allah (swt) is exalted in the Muslim and the rest of the world.
In regard with some of the ahadith over isolation from the people, and that confining oneself to adhere to the matters of personal worship, these ahadith do not serve as an evidence that permits abstaining from establishing a Khaleefah nor removes the sin due to this abstaining. When somebody studies these ahadith thoroughly he finds them related to the adherence to the deen rather than permitting the abandonment of establishing a Khaleefah for Muslims. For example, al-Bukhari narrated about Bisr ibn Obaydellah al-Hadhrami that he heard Abu Idrees al-Khoolani say that he heard Huthaifah ibn al-Yaman saying:
«كان الناس يسألون رسول الله r عن الخير وكنت أسأله عن الشر مخافة أن يدركني، فقلت يا رسول الله إنّا كنا في جاهلية وشر فجاءنا الله بهذا الخير فهل بعد هذا الخير من شر ؟ قال نعم، قلت وهل بعد ذلك الشر من خير ؟ قال نعم، وفيه دخن، قلت وما دخنه ؟ قال قوم يهدون بغير هديي تعرف منهم وتنكر، قلت فهل بعد ذلك الخير من شر ؟ قال نعم، دعاة على أبواب جهنم من أجابهم إليها قذفوه فيها، قلت يا رسول الله صفهم لنا، قال هم من جلدتنا، ويتكلمون بألسنتنا، قلت فما تأمرني إن أدركني ذلك ؟ قال تلزم جماعة المسلمين وإمامهم، قلت فإن لم يكن لهم جماعة ولا إمام، قال فاعتزل تلك الفرق كلها، ولو أن تعض بأصل شجرة حتى يدركك الموت وأنت على ذلك»
“The people used to ask the Prophet of Allah (saw) about the good and I used to ask him about the bad in fear that it might catch me. So I said: O Prophet of Allah! We were in times of jahilliyah and mischief then Allah brought us this good, so is there any mischief after this good? He (saw) said: Yes. I said: Will there be any good after that mischief? He said: Yes, and it has smoke. I said: What is its smoke? He said: (Some) people guide without any guidance, you recognise some (from them) and deny some. I said: Will there be a mischief after that good? He said: Yes, (some) people who invite at the doors of hell, whoever accepted their invitation they throw him in it (hell). I said: O Prophet of Allah, describe them to us. He said: They are of our own skin (of our people) and talk our language. I said: What do you order me to do if that (matter) caught me? He said: Adhere to the jama‘ah of Muslims and their Imam. I said: What if the Muslims have no jama‘ah nor an Imam? He said: Then you abandon all those groups, even if you have to grab with your teeth the trunk of a tree till death comes to you as such.”
This hadith is clear in its expression that the Prophet (saw) orders Muslims to adhere to the jama‘ah of Muslims and to adhere to their Imam, and to leave those who invite people to the doors of hell. When the questioner asked him that in case the Muslims have no Imam and no jama‘ah what he has to do in regard with those who call at the doors of hell, the Prophet (saw) ordered him to abandon these groups, not to disassociate himself from the Muslims nor to abstain from the action for establishing an Imam. So his order is clear, disassociate yourself from all those groups, and he emphasised the dissociation of those groups even to the extent that his isolation from them would make him clench to the trunk of a tree until death comes to him. It means adhere to your deen by staying away from the misleading callers who are at the doors of hell. In this hadith there is no excuse or permission (for anybody) to abandon the work for establishing a Khaleefah, it is, rather, confined to the command of adhering to the deen and abandoning the callers at the doors of hell, and the sin will remain on him if he does not work to establish a Khaleefah. So he is ordered to abandon the misleading groups in order to save his deen from the callers of the misguidance, even if he had to clench to the trunk of a tree, but not to distance himself from the Muslim community and abandon the work for establishing the laws of the deen and establishing an Imam for Muslims.
Another example is what al-Bukhari narrated about Abu Said al-Khudri, who said:
«يوشك أن يكون خير مال المسلم غنم يتبع بها شعف الجبال ومواقع القطر يفر بدينه من الفتن»
The Messenger of Allah (saw) said: "The best wealth of the Muslim is imminent to be sheep with which he follows the summits of mountains and the rain falls to save his deen from the affliction.”
This does not mean that one should isolate oneself from the Muslim community and abandon practising the divine laws and establishing a Khaleefah for Muslims when there is no Khilafah on earth. This hadith rather explains what is the best wealth of the Muslim at the times of temptation, it does not encourage anyone to distance himself from the Muslims and isolate the people.Accordingly, no Muslim on the face of this earth has an excuse to abandon the duty of establishing the deen which Allah (swt) has ordered, that is, the establishment of a Khaleefah for Muslims, when there is no Khilafah on the earth, and no one to implement the hudood (limits) of Allah (swt) to protect the sanctities of Allah (swt), and no one to implement the laws of the deen and unify the Muslim community under the banner of La ilaha illa Allah, Muhammad ur-Rasul Allah. There is no permission in Islam to abandon the work for this duty until it is indeed completed.