This hadeeth was narrated by Muslim (145) from Abu Hurayrah (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Islam began as something strange and will revert to being strange as it began, so give glad tidings to the strangers.”
Al-Sindi said in Hashiyat Ibn Majah:
“Strange” refers to the small number of its adherents. The basic meaning of ghareeb (a stranger) is being far from one's homeland. “And will revert to being strange” refers to the small number of those who will adhere to its teachings even though its followers are many. “So give glad tidings to the strangers” means those who follow its commands. “Tooba (glad tidings)” has been interpreted as meaning Paradise or a great tree in Paradise. This shows that supporting Islam and following its commands may require leaving one's homeland and being patient in bearing the difficulties of being a stranger, as was the case in the beginning.
In Sharh Saheeh Muslim, Al-Nawawi quoted al-Qadi ‘Iyad as saying concerning the meaning of this hadeeth:
“Islam began among a few individuals, then it spread and prevailed, then it will reduce in numbers until there are only a few left, as it was in the beginning.”
It says in Fatawa al-Lajnah al-Daimah, 2/170:
The meaning of this hadeeth is that Islam began as something strange, when the Messenger of Allah (peace and blessings of Allah be upon him) called people to Islam, but no one responded except a few here and there. At that time it was something strange because its people were like strangers amongst others and they were few in number and weak, in contrast to the great numbers and strength of their enemies who persecuted the Muslims. Then some of them migrated to Abyssinia, fleeing for the sake of their religion from tribulation and to save themselves from persecution and oppression, and the Messenger of Allah (peace and blessings of Allah be upon him) migrated at Allah’s command to Madeenah, after suffering intense persecution and in the hope that Allah would give him people to support him in his call and support Islam. Allah fulfilled his hopes, granted victory to his troops and supported His slave.
The Islamic state was established and Islam spread, with the help of Allah, throughout the land; Allah made the word of kufr (disbelief) lowest and the word of Allah is (always) uppermost, for Allah is Almighty, All-Wise, and honour, power and glory belong to Allah, and to His Messenger (peace and blessings of Allah be upon him), and to the believers [cf al-Munafiqoon 63:8]. This continued for a long time, then division and dissent spread among the Muslims and weakness and failure increased gradually, until Islam once again became something strange as it was in the beginning. But this is not because of their small numbers, because at that time they will be many, rather it is because they do not adhere to their religion or cling to the Book of their Lord and the teachings of the Messenger of Allah (peace and blessings of Allah be upon him), apart from those whom Allah wills. So they become distracted and turn to competing in worldly matters, like those who came before them, and they fight amongst themselves for leadership. So the enemies of Islam found a way in and they colonized their lands, humiliated their people and treated them badly. This is the way in which Islam returned to being strange as it was in the beginning.
A number of scholars – including Shaykh Muhammad Rasheed Rida – thought that this hadeeth gives glad tidings of a second victory of Islam after it becomes something strange again. They base this on the metaphor used by the Prophet (peace and blessings of Allah be upon him) when he said, “… will revert to being strange as it began.” So just as following the initial strangeness and alienation the Muslims were victorious and Islam spread, this will happen again after the second period of strangeness and alienation.
This view is more likely to be correct, and is supported by what is proven in the ahadeeth (reports) about the Mahdi and the descent of ‘Eesa (peace be upon him) at the end of time, when Islam will spread and the Muslims will be victorious, and kufr and the kafirs (non-Muslims) will be defeated.
And Allah is the Source of strength. May Allah send blessings and peace upon our Prophet Muhammad and upon his family and companions.