"The disagreement among my Ummah is a mercy."
the Muhaddith Imaam al-Albaanee says in Silsilah al-Ahaadeeth ad-Da`eefah wa'l-Mawdoo`ah (58-62):
Laa Asla Lahu (Baseless). The muhadditheen have tried to find an isnaad (chain of narration) for it but have not found one, to the extent that Suyooti said in his al-Jaami` as-Sagheer,
"Perhaps it was collected in one of the books of the huffaadh which did not reach us!"
This suggestion is very far-fetched, since it would mean that some of the sayings of the Prophet (sal-Allaahu 'alayhe wa sallam) have been lost to the ummah forever, something which is not permissible for a Muslim to believe. Manaawi quoted Subki as saying,
"It (i.e. the saying) is not known to the muhadditheen and I cannot find any isnaad for it, whether saheeh, da`eef or mawdoo`", and this was endorsed by Shaykh Zakareeyyah al-Ansaari in his notes on Tafseer al-Baidaawi [92/2].
Further, the meaning of this hadeeth is also incorrect as shown by the verifying scholars, hence Ibn Hazm says in al-Ihkaam fi Usool al-Ahkaam [5/64] after indicating that it is not a hadeeth,
"This is one of the most incorrect sayings possible, since if ikhtilaaf were a mercy, then agreement would be a punishment, something which no Muslim would say, because there can only be agreement or disagreement, and there can only be mercy or punishment."
Shaykh al-Albaanee also said in his book The Prophets Prayer Described:
Firstly: This hadeeth is not authentic; in fact, it is false and without foundation. Allaamah Subki said,
"I have not come across an authentic or weak or fabricated chain of narration for it", i.e. no chain of narrators exists for this "hadeeth"!
It has also been related with the wordings: "... the difference of opinion among my Companions is a mercy for you" and "My Companions are like the stars, so whichever of them you follow, you will be guided." Both of these are not authentic: the former is very feeble; the latter is fabricated.
Secondly: This hadeeth contradicts the Glorious Qur'aan, for the aayaat forbidding division in the Deen (religion) and enjoining unity are too well-known to need reminding. However, there is no harm in giving some of them by way of example: Allaah says:
"... and do not fall into disputes, lest you lose heart and your power depart." [Soorah al-Anfaal, 8:46]
"And do not be among those join deities with Allaah, those who split up their Deen and become sects - each party rejoicing with what it has!" [Soorah ar-Room, 30:31-2]
"But they will not cease to differ, except those on whom your Lord bestows His Mercy." [Soorah Hood, 11:118-9]
Therefore, if those on whom your Lord has mercy do not differ, and the people of falsehood differ, how can it make sense that differing is a mercy?!
Hence, it is established that this hadeeth is not authentic, neither in the chain of narration, nor in meaning; therefore, it is clear and obvious that it cannot be used to justify resistance towards acting on the Book and the Sunnah, which is what our Imaams have commanded us anyway.