Disputing, after the Clear Signs have come, indicates Deviation 

Allah says; 

كَانَ النَّاسُ أُمَّةً وَاحِدَةً فَبَعَثَ اللّهُ النَّبِيِّينَ مُبَشِّرِينَ وَمُنذِرِينَ وَأَنزَلَ مَعَهُمُ الْكِتَابَ بِالْحَقِّ لِيَحْكُمَ بَيْنَ النَّاسِ فِيمَا اخْتَلَفُواْ فِيهِ وَمَا اخْتَلَفَ فِيهِ إِلاَّ الَّذِينَ أُوتُوهُ مِن بَعْدِ مَا جَاءتْهُمُ الْبَيِّنَاتُ بَغْيًا بَيْنَهُمْ

Mankind was one community and Allah sent Prophets with glad tidings and warnings, and with them He sent down the Scripture in truth to judge between people in matters wherein they differed. And only those to whom (the Scripture) was given differed concerning it, after clear proofs had come unto them, through hatred, one to another.

Ibn Jarir reported that Ibn Abbas said,

"There were ten generations between Adam and Nuh, all of them on the religion of Truth. They later disputed so Allah sent the Prophets as warners and bringers of glad tidings." He then said that this is how Abdullah read the Ayah:

كَانَ النَّاسُ أُمَّةً وَاحِدَةً فَاخْ
 
تَلَفُوا


The people were one Ummah and they then disputed.

Al-Hakim recorded this in his Mustadrak and said, "Its chain of narrators is Sahih, but they (Al-Bukhari and Muslim) did not record it."

Abu Jafar Razi reported that Abu Al-Aliyah said that Ubayy bin Ka`b read the Ayah as:

كَانَ النَّاسُ أُمَّةً وَاحِدَةً فَاخْتَلَفُوا
 
فَبَعَثَ اللّهُ النَّبِيِّينَ مُبَشِّرِينَ وَمُنذِرِينَ


The people were one Ummah and they then disputed and Allah sent the Prophets as warners and bringers of glad tidings.

Abdur-Razzaq said that Ma`mar said that Qatadah said that;

Allah's statement:
كَانَ النَّاسُ أُمَّةً وَاحِدَةً
 (Mankind was one community) means; "They all had the guidance. Then:
فَاخْتَلَفُوا
فَبَعَثَ اللّهُ النَّبِيِّينَ
 (They disputed and Allah sent Prophets). The first to be sent was Nuh."

Abdur-Razzaq reported that Abu Hurayrah commented on:
فَهَدَى اللّهُ الَّذِينَ امَنُواْ لِمَا اخْتَلَفُواْ فِيهِ مِنَ الْحَقِّ بِإِذْنِهِ
 (Then Allah by His leave guided those who believed to the truth of that wherein they differed), saying that the Prophet said:

نَحْنُ الاخِرُونَ الاَْوَّلُونَ يَوْمَ الْقِيَامَةِ نَحْنُ أَوَّلُ النَّاسِ دُخُولاً الْجَنَّــةَ بَيْدَ أَنَّهُم أُوتُوا الْكِتَابَ مِنْ قَبْلِنا وأُوتِينَاهُ مِن بَعْدِهِمْ فَهَداَنا اللهُ لِمَا اخْتَلَفُوا فِيهِ مِنَ الْحَقَّ بِإِذْنِهِ فَهَذَا الْيَوْمُ الَّذِي اخْتَلَفُوا فِيهِ فَهَدَانَا اللهُ لَهُ فَالنَّاسُ لَنَا فِيهِ تَبَعٌ فَغدًا لِلْيَهُودِ وَبَعْدَ غَدٍ لِلنَّصَارَى

We are the last (nation), but the first (foremost) on the Day of Resurrection. We are the first people to enter Paradise, although they (Jews and Christians) have been given the Book before us and we after them. Allah has guided us to the truth wherever they disputed over it. This is the day (Friday) that they disputed about, Allah guided us to it. So, the people follow us, as tomorrow is for the Jews and the day after is for the Christians.

Ibn Wahb related that Abdur-Rahman bin Zayd bin Aslam said that his father said about the Ayah:
فَهَدَى اللّهُ الَّذِينَ امَنُواْ لِمَا اخْتَلَفُواْ فِيهِ مِنَ الْحَقِّ بِإِذْنِهِ
 (Then Allah by His leave guided those who believed to the truth of that wherein they differed), 

"They disputed about the day of Congregation (Friday). The Jews made it Saturday while the Christians chose Sunday. Allah guided the Ummah of Muhammad to Friday. 

They also disputed about the true Qiblah. The Christians faced the east while the Jews faced Bayt Al-Maqdis. Allah guided the Ummah of Muhammad to the true Qiblah (Ka`bah in Makkah). 

They also disputed about the prayer, as some of them bow down, but do not prostrate, while others prostrate, but do not bow down. Some of them pray while talking and some while walking. Allah guided the Ummah of Muhammad to the truth. 

They also disputed about the fast; some of them fast during a part of the day, while others fast from certain types of foods. Allah guided the Ummah of Muhammad to the truth. 

They also disputed about Ibrahim. The Jews said, `He was a Jew,' while the Christians considered him Christian. Allah has made him a Haniyfan Musliman. Allah has guided the Ummah of Muhammad to the truth. 

They also disputed about `Isa. The Jews rejected him and accused his mother of a grave sin, while the Christians made him a god and the son of God. Allah made him by His Word and a spirit from (those He created) Him. Allah guided the Ummah of Muhammad to the truth." 

Allah then said:
 
بِإِذْنِهِ
by His leave,

According to Ibn Jarir meaning,

`By His knowledge of them and by what He has directed and guided them to.'

Also:
 
وَاللّهُ يَهْدِي مَن يَشَاء

And Allah guides whom He wills,

means from among His creation.

Allah said,
 
إِلَى صِرَاطٍ مُّسْتَقِيمٍ
 
 
to the straight way.

meaning, He commands the decision and the clear proof.

Al-Bukhari and Muslim reported that Aishah narrated that;

when Allah's Messenger used to wake up at night to pray, he would say:

اللَّهُمَّ ربَّ جِبْرَايِيلَ وَمِيكَايِيلَ وَإِسْرَافِيلَ فَاطِرَ السَّموَاتِ وَالاَْرْضِ عَالِمَ الْغَيْبِ وَالشَّهَادَةِ أَنْتَ تَحْكُمُ بيْنَ عِبَادِكَ فِيمَا كَانُوا فِيهِ يَخْتَلِفُونَ اهْدِنِي لِمَا اخْتُلِفَ فِيهِ مِنَ الْحَقِّ بِإِذْنِكَ إِنَّكَ تَهْدِي مَنْ تَشَاءُ إِلى صِرَاطٍ مُسْتَقِيم

O Allah, the Lord of (angels) Jibril, Mikhail and Israfil, Creator of the heavens and earth and Knower of the seen and the unseen. You judge between Your servants regarding what they have disputed in, so guide me to what have been the subject of dispute of the truth by Your leave. Indeed, You guide whom You will to the straight path. 

A Du`a (supplication) reads:

اللَّهُمَّ أَرِنَا الْحَقَّ حَقًّا وَارْزُقْنَا اتِّبَاعَهُ وَأَرِنَا الْبَاطِلَ بَاطِلً وَارْزُقْنَا اجْتنِاَبَهُ وَلَا تَجْعَلْهُ مُلْتَبِسًا عَلَيْنَا فَنَضِلَّ وَاجْعَلْنَا لِلْمُتَّقِينَ إِمَامًا

O Allah! Show us the truth as truth, and bestow adherence to it on us. Show us the evil as evil, and make us stay away from it, and do not confuse us regarding the reality of evil so that we will not be led astray by it, and make us leaders for the believers.