Is the sin of inadvertently speaking during prayer lifted only from the speaker due to the hadith: "Mistakes, forgetfulness, and what they are coerced into have been lifted from my Ummah," and does he have to repeat that prayer?

The aforementioned Hadith was narrated by Ibn Majah and others from Ibn Abbas, who reported that the Prophet, peace and blessings be upon him, said: "Indeed, Allah has pardoned for my Ummah their mistakes, their forgetfulness, and what they are coerced into."

Human speech is not permissible during prayer. However, if it occurs due to forgetfulness, the prayer is not invalidated, the doer is not sinful, and there is no obligation to make up or repeat the prayer. Imam An-Nawawi said: "If one speaks out of forgetfulness and their speech is not prolonged, then our madhhab is that their prayer is not invalidated, and this is also the view of the majority of scholars."

However, it is prescribed for the person to perform the prostration of forgetfulness (sujood as-sahw) after the tasleem, if they are an Imam or praying individually.