A speech impediment such as a lisp refers to the inability to correctly pronounce one or more letters, resulting in misarticulation. In terms of an individual’s personal acts of worship, such a condition—if it cannot be treated—does not affect their validity. Otherwise, the person would be burdened with something beyond their capacity. As stated in the Qur’an: “Allah does not burden a soul beyond its capacity” (al-Baqarah 2:286) and “He has not placed upon you in the religion any hardship” (al-Hajj 22:78).
However, when it comes to leading prayer (imamate) or reciting in a communal setting such as a mukabele, the extent to which the speech impediment affects the recitation must be considered. If a person is unable to pronounce multiple letters correctly and this affects the meaning of the Qur’anic recitation, they should refrain from leading prayer or reciting in front of others.
If the effect is minor—for example, pronouncing the letter “sīn” (س) as “thā” (ث)—and does not invalidate the prayer, then the person may lead prayer or recite, provided it does not cause discomfort within the congregation. Especially if the recitation is shared with others and the person is responsible for only a portion, there is no need to exclude them from this act of worship. By the will of Allah, their recitation will be accepted.