because there is not a space in the heavens the width of four fingers except that an angel is standing, bowing, or prostrating to Allah.
His statement, “It is recommended for the reciter,” is supported by the fact that the Prophet, may Allah’s blessings and peace be upon him, would prostrate whenever he came to a verse of prostration. When the Messenger, may Allah’s blessings and peace be upon him, performs an act as an act of worship, this indicates that it is recommended. Hence, one of the principles of legal theory is that an act performed by the Messenger, may Allah’s blessings and peace be upon him, as an act of worship indicates recommendation rather than obligation—unless it is accompanied by a command, or serves as an explanation of a command, or there are similar contextual indications that establish its obligation. Mere action, however, indicates recommendation.
Ibn Umar narrated: “The Prophet, may Allah’s blessings and peace be upon him, would recite to us a surah containing a verse of prostration, and he would prostrate and we would prostrate with him, until none of us could find a place for his forehead.” (1) That is, they would prostrate, and because they were close to the Prophet, may Allah’s blessings and peace be upon him, they would crowd together, since one who prostrates occupies more space than one who is seated, until one of them could not find a place on which to rest his forehead in prostration. This proves that it is recommended, as does the previously mentioned report from Umar, may Allah be pleased with him. (2)
The one who listens attentively, as opposed to one who merely hears …
His statement, “the one who listens attentively,” is supported by the hadith of Ibn Umar, may Allah be pleased with him and his father: they would prostrate along with the Messenger of Allah, may Allah’s blessings and peace be upon him.
His statement, “as opposed to one who merely hears,” means that it is not recommended for one who merely hears to prostrate. The difference between one who listens attentively and one who merely hears is that the former pays attention to the reciter and follows the recitation, whereas the latter hears something without deliberately listening to it.