Al Salamu 'Alaykum.
Some of the Companions [Sahaba], Followers [Tabi’in] and those who came after them [Taba Tabi’in] used to recite basmala, while others among them there were those who did not recite it; some of them used to read it loudly and others did not read it loudly. Some of them read qunut in Fajr prayer while others did not read it in Fajr prayer. Among them there were those who used to perform ablution [wudu] because of cupping, nose bleeding and vomiting, while others did not make wudu because of those things. Some of them performed wudu for lustfully touching the penis and women, while others would not perform wudu because of such things. Some of them used to perform wudu for eating the meat of camel while others did not perform wudu because of that.
Despite all these differences they used to pray behind each other. For example, Abu Hanifa, his companions, Shafi’i and others prayed behind the Imams of Madina who were Malikis and of other inclinations, even though they did not recite basmala in prayers, secretly or loudly.
Once Harun al-Rashid led the prayer after being cupped, and Imam Abu Yusuf [al-Hanafi] prayed behind him but did not repeat the prayer. The former was given fatwa by Imam Malik that in his situation wudu was not necessary for him. Imam Ahmad b. Hanbal considered wudu necessary because of nose bleeding and cupping. He was asked: “If the Imam had the bleeding and did not perform wudu afterwards, would you pray behind him?” He replied: “Why shouldn’t I pray behind Imam Malik and Sa’id b. Al-Musayyab?”
It is reported that Abu Yusuf and Muhammad used to say takbir in ‘iddain prayers on the pattern of Ibn ‘Abbas because Harun al-Rashid liked the takbir of his grandfather. When Shafi’i prayed the Morning Prayer near the grave Abu Hanifa; he did not read qunut as a token of respect. He also said: “Perhaps we have descended to the madhhab of the people of ‘Iraq”. Malik said the same to Mansur and Harun al-Rashid what we have already mentioned about him before.
It is reported in kitab al-Bazaziah of Muhammad b. Shihab b. Bazaz (d. 872AH) about the second Imam i.e. Abu Yusuf, that after bathing in a public bath he led the people in Friday prayer. After he finished the prayer and the people dispersed, he was informed of a dead mouse in the well of the bath. In response, he said: “In that case we will follow the view of our Madinian brethren, which says ‘When the water reaches qullatain it does not get impure’”.
Taken from: Differences of Opinion in Fiqh [Al-Insaf fi bayan sabab al-ikhtilaf] by Shah WaliAllah al-Dihlawi.
Wa salamu 'alaykum.