In the name of Allah, the Most Gracious, the Most Merciful

Issues Related to Prohibited Matters in Prayer (In the Light of Ḥadīth)

Placing the hands on the waist during prayer is prohibited:

    Abū Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ forbade placing the hands on the sides during prayer.
    (Ṣaḥīḥ Muslim, Ṣaḥīḥ al-Bukhārī)

Cracking the fingers or interlacing the fingers during prayer is prohibited:

    Kaʿb ibn ʿUjrah (may Allah be pleased with him) said that the Messenger of Allah ﷺ said: “When one of you performs wuḍūʾ and proceeds toward the mosque, he should not interlace his fingers while walking, for he is in a state of prayer.”
    (Jāmiʿ al-Tirmidhī, Sunan al-Nasāʾī, Sunan Abī Dāwūd)

One is instructed to avoid yawning during prayer as much as possible:

    Abū Saʿīd al-Khudrī (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ said: “When one of you yawns during prayer, he should restrain it as much as he is able, for at that time Satan enters the mouth.”
    (Ṣaḥīḥ Muslim)

Raising the gaze toward the sky during prayer is prohibited:

    Abū Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ said: “People must refrain from raising their eyes toward the sky while supplicating in prayer, otherwise their sight may be snatched away.”
    (Ṣaḥīḥ Muslim)

Covering the mouth during prayer is prohibited:

    Abū Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ forbade “sadal” and covering the mouth during prayer.
    (Sunan Abī Dāwūd, Jāmiʿ al-Tirmidhī)

Gathering garments, arranging the hair, or making unnecessary movements during prayer is prohibited:

    ʿAbdullāh ibn ʿAbbās (may Allah be pleased with him) said that the Prophet ﷺ said: “I have been commanded to prostrate upon seven bones: the forehead”—and he indicated toward his nose with his hand—“the two hands, the two knees, and the toes of the two feet. And I have been commanded that we should not gather our garments or hair during prayer.”
    (Ṣaḥīḥ al-Bukhārī)

Repeatedly removing pebbles from the place of prostration is prohibited:

    Muʿayqīb (may Allah be pleased with him) narrated that regarding the one who levels the ground at the place of prostration, the Prophet ﷺ said: “If it must be done, then do it once.”
    (Ṣaḥīḥ al-Bukhārī, Ṣaḥīḥ Muslim)

Looking around during prayer is prohibited:

    Abū Dharr (may Allah be pleased with him) narrated that the Messenger of Allah ﷺ said: “Allah continues to turn toward His servant in prayer so long as he does not look around; when he turns his attention away, Allah turns away from him.”
    (Sunan Abī Dāwūd, Sunan al-Nasāʾī)

Performing prostration upon a pillow or offering prayer upon a mattress is prohibited:

    Ibn ʿUmar (may Allah be pleased with him) narrated that the Prophet ﷺ said to a sick person who was praying upon a pillow: “Remove it. If you are able to prostrate upon the ground, then do so; and if you are unable to prostrate upon the ground due to illness, then perform the prayer by gesture, and for prostration lower your head more than for rukūʿ.”
    (Ṭabarānī)