Hadith: I have divided prayer between Myself and My servant into two halves, and My servant shall have what he has asked for

عن أبي هريرة عن النبي صلى الله عليه وسلم قال: «من صلى صلاة لم يقرأ فيها بأم القرآن فهي خداج -ثلاثًا- غير تمام» فقيل لأبي هريرة: إنا نكون وراء الإمام؟ فقال: اقرأ بها في نفسك، فإني سمعت رسول الله صلى الله عليه وسلم يقول: «قال الله تعالى: قسمت الصلاة بيني وبين عبدي نصفين، ولعبدي ما سأل، فإذا قال العبد: {الحمد لله رب العالمين} قال الله تعالى: حمدني عبدي، وإذا قال: {الرحمن الرحيم} قال الله تعالى: أثنى علي عبدي، وإذا قال: {مالك يوم الدين}، قال: مجدني عبدي -وقال مرة فوَّض إلي عبدي- فإذا قال: {إياك نعبد وإياك نستعين}قال: هذا بيني وبين عبدي، ولعبدي ما سأل، فإذا قال: {اهدنا الصراط المستقيم صراط الذين أنعمت عليهم غير المغضوب عليهم ولا الضالين} قال: هذا لعبدي ولعبدي ما سأل».
[صحيح] - [رواه مسلم]

Abu Hurayrah (may Allah be pleased with him) reported: The Prophet (may Allah’s peace and blessings be upon him) said: "Whoever offers a prayer in which he does not recite Umm al-Qur'an (Surat al-Fātihah), it is deficient, it is deficient, it is deficient, incomplete." It was said to Abu Hurayrah: "O Abu Hurayrah, we sometimes pray behind the Imām." He said: "Recite it to yourself, for I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: 'Allah Almighty said: 'I have divided prayer between Myself and My servant into two halves, and My servant shall have what he has asked for.' When the servant says '{All praise be to Allah, the Lord of the worlds}', Allah Almighty says: 'My servant has praised Me.' And when he says '{The Most Compassionate, the Most Merciful}', Allah Almighty says: 'My servant has extolled Me.' And when he says '{Master of the Day of Judgment}', Allah Almighty says: 'My servant has glorified Me' - And He also says: 'My servant entrusted his affairs to Me' - And when he says, '{You alone we worship, and You alone we ask for help}', He says: 'This is between Me and My servant, and My servant shall have what he has asked for.' And when he says '{Guide us to the straight path, the path of those whom You have blessed; not of those who incurred Your Wrath, or of those who went astray}', He says: 'This is for My servant, and My servant shall have what he has asked for.'"
Sahih/Authentic. - [Muslim]

Explanation

Abu Hurayrah reported the Prophet's Hadīth saying that if a person offers a prayer - whether he is an Imām, being led in prayer, or praying alone, and whether the prayer's recitation is audible or inaudible, and be it obligatory or supererogatory - without reciting Umm al-Qur'an, i.e., Surat al-Fātihah, his prayer is deficient and incomplete; that's it has such deficiency that renders it null and void. He said this three times. This is a strong proof for the obligation of reciting Surat al-Fātihah in every prayer. It was said to Abu Hurayrah: O Abu Hurayrah, we sometimes pray behind the Imām. That's sometimes we follow the Imām in prayer, and he recites Surat al-Fātihah. So, is it wrong if we do not recite it? He said: Recite it to yourself, which means: Recite Surat al-Fātihah secretly; that's utter it inaudibly. This, however, should not be taken to mean: Recite it within your heart, without utterance. This is not regarded as recitation, by consensus among language experts. Then, Abu Hurayrah (may Allah be pleased with him) moved from one proof to another, for corroboration. He said: I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: "Allah Almighty said: 'I have divided prayer between Myself and My servant into two halves.'" By 'prayer' He meant Surat al-Fātihah. He called it as such because prayer is not valid without it. Thus, the name of a whole thing is used to refer to a part of it. The division here pertains to meanings. The first half contains praise of Allah and glorification of Him and affirmation of His oneness. In the second half, the servant acknowledges his own weakness and need before his Lord and he asks Him to guide him and help him hold onto guidance. This division provides evidence that "In the name of Allah, the Most Compassionate, the Most Merciful" is not part of Surat al-Fātihah; rather, it is a separate verse at the start of every Surah. His statement "And My servant shall have what he has asked for" is a promise from Allah Almighty that He will answer the supplication of His servant. When the servant says "{All praise be to Allah, the Lord of the worlds}", Allah Almighty says: "My servant has praised Me." That's he describes Me by the attributes of My perfection and majesty. And when he says "{The Most Compassionate, the Most Merciful}", Allah Almighty says: "My servant has praised Me." That's he repeated the excellent description, as he acknowledge My overall favors upon My servants. And when he says "{Master of the Day of Judgment}", Allah Almighty says: "My servant has extolled Me." That's he proclaims My glory, greatness, and honor. His statement "And He also says: "My servant entrusted his affairs to Me" means that He says both phrases. But, he says "My servant entrusted his affairs to Me" less often. And when he says, "{You alone we worship, and You alone we ask for help}", He says: "This is between Me and My servant, and My servant shall have what he has asked for." In this phrase, the servant proclaims Allah's oneness and greatness and seeks help from Him in all His affairs. And when he says "{Guide us to the straight path, the path of those whom You have blessed; not of those who incurred Your Wrath, or of those who went astray}", He says: "This is for My servant, and My servant shall have what he has asked for." In this, the servant supplicates for himself, and this is a promise from Allah Almighty that He will respond to him and give him the help he has asked for. We know from this Hadīth that Allah Almighty has called "Surat al-Fātihah" prayer, and divided it into two halves between Himself and His servant, and that whoever does not recite it in prayer, his prayer is invalid. So, everyone must recite in prayer, whether he is an Imām, being led in prayer, or praying alone.