Assalamu alaykum. I was told recently that in the pronunciation of Takbeerat Al-Ihraam, one must pronounce it 'Allaahu Akbar' and not 'Allaahuwakbar' or else it invalidates your prayer. I have much difficulty in telling the two apart, sometimes I repeat my Takbeerat Al-Ihraam because I cannot tell whether I said it right or not.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The addition of the extra letter "Waw" in the Takbeer to be pronounced 'Allaahuwakbar' instead of 'Allaahu Akbar' is considered a clear mistake regardless of whether it be in pronunciation or writing. This addition invalidates the prayer according to many scholars if the worshiper makes it while reciting Takbeerat Al-Ihraam (opening Takbeer in prayer) because it is one of the pillars of the prayer. It must be pronounced correctly with no omission, addition, or alteration.

An-Nawawi wrote, "The praying person should beware of adding an extra pause between the two words of Takbeer (to pronounce it: 'Allaah - pause - Akbar' instead of 'Allaahu Akbar' with no pause) or make an addition that changes the meaning. The Takbeer is invalid if he pauses, elongates the Hamzah of Allaah (pronouncing it 'Aallaah'), elongates the word Akbar to be pronounced 'Akbaaar', or adds an extra Waw whether with or without a diacritical mark)." [Al-Majmoo‘]

However, the Maalikis held that adding an extra Waw in Takbeerat Al-Ihraam so that it be pronounced 'Allaahuwakbar' does not invalidate the prayer. The Maaliki scholar An-Nafraawi wrote, "The Takbeerat Al-Ihraam is not invalidated if the person adds an extra Waw before the word Akbar,  replaces the Hamzah with a Waw letter, prolongs the Haa' sound at the end of Allaahu (to be pronounced Allaahoo), makes a brief pause between the word Allaahu and the word Akbar, or alters the Sukoon (which indicates the absence of short vowels) at the end of the word Akbar to the short vowel Dhammah (to be pronounced Akbaru)." [Al-Fawaakih Ad-Dawaani]

Hence, if the questioner finds difficulty in pronouncing Takbeerat Al-Ihraam correctly without adding an extra Waw, he may follow the Maaliki school of Fiqh in this regard. According to the Maaliki view, his prayer is valid, especially given the fact that he finds difficulty in pronouncing Takbeerat Al-Ihraam correctly, driving him to repeat it many times to pronounce it correctly.

It is permissible for the lay Muslim to follow the views of any of the reliable schools of Fiqh, and he is not obliged to follow one specific school of Fiqh in all matters.

Ibn Hajar Al-Haytami wrote, "The preponderant view is that it is allowable for the lay Muslim to follow any of the four Imaams or any other scholar whose views on an issue have been duly preserved and documented while the governing criteria and considerations in reaching those views have been clearly identified." [Tuhfat Al-Muhtaaj]

Allaah knows best.