What is the ruling on the prayer of a person praying alone or an Imam if he makes a mistake in reciting Al-Fatiha by saying (wa-li-ḍḍāllīn) instead of (wa-lāḍ-ḍāllīn)? Is he required to repeat it, and how does he repeat prayers whose number he does not know? What is the ruling on the prayer of someone who makes a mistake in the rules of Tajwid or the vocalization (tashkīl) in Al-Fatiha?

Scholars have differed on the invalidity of prayer due to omitting a shaddah (doubling sign) from Al-Fatihah. The Hanbali and Shafi'i schools of thought hold that it invalidates the prayer because a shaddah stands for two letters, and omitting it leads to a defect in the letter and a change in meaning. As for errors in vocalizing words, if they result in a change of meaning, the prayer is invalidated, such as pronouncing the "kaf" in "Iyyaka" with a kasrah (i) or the "ta'" in "An'amta" with a dammah (u). If the meaning does not change, the prayer is not invalidated. Similarly, prayer is not invalidated by failing to observe the rules of Tajweed. If someone prays while omitting a shaddah from Al-Fatihah and their tongue is unable to pronounce it correctly, their prayer is valid. However, if they are capable, their prayer is invalid, and the prayer of anyone praying behind them is not valid if that person is capable of correct recitation. Invalidated prayers must be repeated. If the number of such prayers is unknown, one should make up what they believe will clear their conscience.