Second Caliph Umar ibn al Khattab (la) introduced numerous innovations in Islam (that did not exist during the time of the Prophet Muhammad (s) and forbade things which the Prophet himself had enjoined. To quote a few:
1) He initiated the congregational Tarweeh prayer in the month of Ramzan, which the Prophet himself had forbidden it upon the community (Imam al- Bukhari, “Sahih”, vol. 3 and 8)
2) He added the following line into the adhan of the Fajr prayers, “As-Salatu khairum minan nawm (Prayer is better than sleep)” (Imam al-Malik, “al-Muwatta”)
3) Pointing the index finger during recitation of salutations (salam) in prayers towards the Kaabah (Shibli al-Nomani, “al-Farooq”; Shah Waliyullah Muhaddith al-Dehlawi, “Izalatul Khifa”, vol. 3)
4) Changed the ruling of the Noble Prophet by treating three pronounced divorces in one sitting and same time, as one (Imam al-Muslim, “Sahih”)
5) The first one to award himself the title of Amirul Mumeneen (Imam al-Bukhari, “Sahih”; Ibn Khaldun, “al-Muqaddamah”; Shibli Numani, “al-Farooq”)
6) Entered into a treaty with the Christians of Syria in which he offered them entirely new terms by drafting a document that sought to humiliate them, quite contrary to the Prophet’s dealings with them (Ibn Taymiyah, “al-Fatawa”; Ibn Hazm, “al-Muhalla”; Shibli al-Numani, “al-Farooq”)
7) Ordered the killing of Magians (Zoroastrian). (Abu Dawud, “al-Sunan”, bk. 19)
8) Depriving the Ahlul Bayt of the Prophet a share from the khums after his death
9) Despatching cruel commanders (like Khalid b. Walid) with drawn swords and large troops to expand his dominion under the pretext of spreading Islam far and wide
10) Forbidding the writing of Prophetic traditions (Hadith)
11) Prohibiting the pronouncement of “Hayya ala khairil Amal” (come towards the best deed As-Salat) in the adhan (Imam al-Malik, “al-Muwatta”; al-Taftazani, “Shahr al-Maqasid”; al-Qushaji, “Shahr al-Tajrid”; Ali al-Halabiyah, “Siratul Halabiyah”
12) Prohibited the mutah (temporary marriage) of Hajj and mutah with women while both of these were permitted during the lifetime of the Prophet (Imam al-Bukhari, “Sahih”; Imam al-Muslim, “Sahih”, vol. 1; al-Taftazni, “Shahr al-Maqasid”; al-Qushaji, “Shahr al-Tajrid”). He most audaciously declared, “There are two mutah which existed in the time of the Prophet of Allah and during Abu Bakr which I have banned and I will punish those who disobey my orders – these two are the mutah of the Hajj and the mutah of the women.” Imam Ali says, “If Umar had not forbidden mutah, there would have been only a few unfortunate men who committed fornication.” (al-Tabari, “al-Tafsir”). Abdullah b. Abbas also comments saying, “Muttah was a blessing that Allah, the Almighty, endowed the nation of Muhammad and had it not been prohibited, no one except the truly perverted ones would have committed adultery.” (Ibn Athar, “al-Nihiyah”; al-Zamakhshari, “al-Faiq”)
13) He forbade the mahr for women to be more than 400 dirhams, even when a woman in the public pointed out a verse from the Quran permitting it. (Jalaluddin al-Suyyti, “Tafsir Durr al-Manthur”, vol. 2; Ibn Kathir, “al-Tafsir”, vol. 1; al-Zamakhshari, “Tafsir al-Kashshif”, vol. 1; Ibn Majah, “al-Sunan” vol. 1; al-Baihaqi, “Sunan al-Kubra”, vol. 1; al-Qastalani “Irshadus Sari Sharh Sahih al-Bukhari” vol. 8; Muttaqi al-Hindi, “Kanzul Ummal” vol. 8; Hakim al-Naishapuri, “al-Mustadrak” vol. 2), and many more acts.
One should refer to the words of the Quran, “And whatever the Apostle give you, accept it, and whatever he prevents you from, keep away from it; and fear (the wrath of Allah); Verily Allah is severe in retribution.” Sura Hashr (59): 7) — however Umar seemed to be heedless of this injunction of the Quran!