Taken from the Blog of Brother Khaldun | http://khaldun.wordpress.c
"Some people often qoute the hadith of the Prophet wherein which he says, the differences within my Ummah is a mercy. However this hadith is not correct.
Shaykh ibn 'Uthaymeen was asked this question and this is the reply he gave:
This is wrong (ie if they mean that the opposite is true, meaning unity is a punishment), because ikhtilaaf is not a mercy and this is due to Allahs statement
وَلاَ يَزَالُونَ مُخْتَلِفِينَ إِلاَّ مَن رَّحِمَ رَبُّكَ
And they will never seize to differ except those whom Allah has mercy upon.
So this shows the weakness in the mentioned hadith. However those who differ and are Mujtahideen (well rooted in knowledge) then they will aquire mercy (from Allah)."
This is the opinion of a scholar, it is not my own writings. Also this Hadith which says that the differences in the Ummah are a mercy was graded as fabricated by Shaykh Albani (Rahimahullah) (see http://islamqa.com/en/ref/
Do not pick and choose between opinions,
Follow the authentic Ahadith.
And Allah (swt) the Most High knows Best.
A Brother's Wise Response to my Post:
It depends on the type of differening. From what I gather from your response is that you are considering this to be in terms of opinions of Fiqh, while to me it is talking about iktilaaf in issues of Aqeedah.
Why do I say that, well there are a few reasons. One such reason is that many times in the life of the Prophet you would find the Sahaba would do ijtihad in an issue and they both would be right in their ijtihad, like in the issue of how they understood the command of the Prophet(saw) to pray when you arrive a certain location, some of them prayed when they arrived and some of them understood from it to pray in the road if the time for salah comes but to go quickly to the destination, neither of them were incorrect.
Also is the statement of the prophet about the Mujtahid who makes ijtihaad and if he is right he gets two rewards and if he is wrong he gets 1.(this is a mercy from Allah in their differing)
However differing in issues of Usool, meaning that which everything else is built upon is not correct, like if we know that the salah is 5 we can't say its four, and if the differing is differing that causes division this is also incorrect, such as the differing of the different sects, because Allah says "Hold on to the rope of Allah and do not be divided".
As for the differences in fiqh issues, most of the time they have a illegitimate difference, and it is not done except that one scholar understood it a different way and applied his ruling, and in the case of the 4 madhabs each madhab has different rules of extracting rulings from the text.
Also you say "Follow the authentic hadith", no doubt this is true, but what then when you have two different authentic hadiths that say the total opposite? Or when you have no authentic hadith but you have hadith's that are hasan, or weak, or other then that? Eventually we as non scholars have to rely on the oppinion of a scholar in issues, and put our trust in someone as to what they deemed to be correct from the text and frequently they differ.
Also different scholars authenticate hadiths in different ways, because of their methodology, etc. So you will find sometimes A hadith is saheeh by tirmidhi that may be weakened by dawud.
Ultimately as Muslims we have to do what Allah says "Ask the people of knowledge if you do not know" , and this also why Sheikh uthaymeen in his fatawa number 114 of book 26 said in certain situations it is wajib upon the person to make taqleed of a scholar(or madhab).