In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Most High] said:

قَدۡ أَفۡلَحَ ٱلۡمُؤۡمِنُونَ (١) ٱلَّذِينَ هُمۡ فِى صَلَاتِہِمۡ خَـٰشِعُونَ (٢) وَٱلَّذِينَ هُمۡ عَنِ ٱللَّغۡوِ مُعۡرِضُونَ (٣) وَٱلَّذِينَ هُمۡ لِلزَّكَوٰةِ فَـٰعِلُونَ (٤)وَٱلَّذِينَ هُمۡ لِفُرُوجِهِمۡ حَـٰفِظُونَ (٥) إِلَّا عَلَىٰٓ أَزۡوَٲجِهِمۡ أَوۡ مَا مَلَكَتۡ أَيۡمَـٰنُہُمۡ فَإِنَّہُمۡ غَيۡرُ مَلُومِينَ (٦) فَمَنِ ٱبۡتَغَىٰ وَرَآءَ ذَٲلِكَ فَأُوْلَـٰٓٮِٕكَ هُمُ ٱلۡعَادُونَ (٧) وَٱلَّذِينَ هُمۡ لِأَمَـٰنَـٰتِهِمۡ وَعَهۡدِهِمۡ رَٲعُونَ (٨) وَٱلَّذِينَ هُمۡ عَلَىٰ صَلَوَٲتِہِمۡ يُحَافِظُونَ (٩) أُوْلَـٰٓٮِٕكَ هُمُ ٱلۡوَٲرِثُونَ (١٠) ٱلَّذِينَ يَرِثُونَ ٱلۡفِرۡدَوۡسَ هُمۡ فِيہَا خَـٰلِدُونَ (١١)

Successful indeed are the believers. Those who offer their Salaat [prayers] with all solemnity and full submissiveness. And those who turn away from Al-Laghw [dirty, false, evil vain talk, falsehood, and all that Allah has forbidden]. And those who pay the Zakaat. And those who guard their chastity (i.e. private parts, from illegal sexual acts), except from their wives or those whom their right hands possess, for then, they are free from blame; but whoever seeks beyond that, then those are the transgressors; those who are faithfully true to their Amanaat [all the duties which Allah has ordained, honesty, moral responsibility and trusts etc.] and to their covenants; and those who strictly guard their (five compulsory congregational) Salawaat [prayers] [at their fixed stated hours]. These are indeed the inheritors. Who shall inherit the Firdaus [Paradise]. They shall dwell therein forever. [Surah Al-Muminoon. Aayaat 1-11]

[ٱلَّذِينَ هُمۡ فِى صَلَاتِہِمۡ خَـٰشِعُونَ- Those who offer their Salaat [prayers] with all solemnity and full submissiveness]: Solemnity in the prayer: It is attentiveness of the heart in the presence of Allaah [The Exalted]; attentive [to the fact that] Allaah is close [i.e. by His knowledge, hearing and sight] and thus the person’s heart becomes submissive, his soul [enters a state] of solemnity, his movements [in the prayer are performed] with repose, he [experiences] little distraction, well behaved in the presence of his Lord, pays attention to everything he says and does in his prayer – from the beginning to the end – and thus all the whispering of shaytaan is repelled, [and likewise] all evil thoughts. This is the essence of the prayer and the aim behind it. It is the type of prayer for which a person is rewarded is in full. [As for the prayer] that is neither performed  with tranquillity nor an attentive heart, then even though the person will gain some reward, however reward is based on the strength [or level] of the heart’s attentiveness. [1]

Allaah [The Most High] said:

وَاسْتَعِينُوا بِالصَّبْرِ وَالصَّلَاةِ ۚ وَإِنَّهَا لَكَبِيرَةٌ إِلَّا عَلَى الْخَاشِعِينَ

الَّذِينَ يَظُنُّونَ أَنَّهُم مُّلَاقُو رَبِّهِمْ وَأَنَّهُمْ إِلَيْهِ رَاجِعُونَ

And seek help in patience and prayer, and truly it is extremely heavy and hard except for those who humble in the presence of their Lord.” They are those who are certain that they are going to meet their Lord, and that to Him they are going to return. [Al-Baqarah: Ayah: 45-46]

Indeed, it [i.e. seeking help in patience and prayer] is heavy upon other than those who are humble before Allaah, because the hearts [of those who are not humble before Allaah] are devoid of love of Allaah, exaltation of Him, glorification of Him and humility in His presence. They have little desire in asking Allaah for the good things of the worldly and the afterlife, and [they have little desire] in seeking His protection from the evil affairs of this life and the next. That is because the presence of the slave’s heart and mind in the prayer, being humble within [the prayer], seeking for perfection in it, disconnecting his mind and heart from everything whilst in the prayer, and striving with great effort to establish and fulfil it, then [all of this takes place] in accordance with the strength of his fervent desire [to please Allaah, hoping for Allaah’s reward and fearing Allaah’s punishment]. [2]

Allaah [The Most High] said:

وَجَعَلۡنَـٰهُمۡ أَٮِٕمَّةً۬ يَہۡدُونَ بِأَمۡرِنَا وَأَوۡحَيۡنَآ إِلَيۡهِمۡ فِعۡلَ ٱلۡخَيۡرَٲتِ وَإِقَامَ ٱلصَّلَوٰةِ وَإِيتَآءَ ٱلزَّڪَوٰةِ‌ۖ وَكَانُواْ لَنَا عَـٰبِدِينَ

And We made them [i.e. Ibraaheem, Ishaaq and Ya’qoob (alayhimus-salaam)] leaders, guiding [mankind] by Our Command, and We inspired in them the doing of good deeds, performing Salaat, and the giving of Zakaat and of Us (Alone) they were worshippers. [Surah Al-Anbiyaa. Aayah 73]

[وَجَعَلۡنَـٰهُمۡ أَٮِٕمَّةً۬  – And We made them leaders]– Meaning: Leaders  who were guides for others to good. [يَہۡدُونَ بِأَمۡرِنَا  – by Our Command]– Meaning: They called people to the religion ordained by Allaah based on Allaah’s command. [Ref 3]

[وَأَوۡحَيۡنَآ إِلَيۡهِمۡ فِعۡلَ ٱلۡخَيۡرَٲتِ   – And We inspired in them the doing of good deeds]– Meaning: They performed good deeds and called people to it. This includes all types of good deeds related to the rights of Allaah and the rights of the people. [وَإِقَامَ ٱلصَّلَوٰةِ وَإِيتَآءَ ٱلزَّڪَوٰةِ‌ۖ– performing Salaat, and the giving of Zakaat]: This is a specific mention of something in connection to a general affair due to the nobility and virtue of these two acts of worship [i.e. Salaah and Zakaat]; because whoever performs them perfectly will establish his religion and whoever neglects them will be more negligent towards other affairs of the religion; and [also because] Salaah is the best of deeds related to the rights of owed to Allaah and Zakaat is the best of deeds related to the rights owed to Allaah’s servants.

[وَكَانُواْ لَنَا عَـٰبِدِين – and of Us (Alone) they were worshippers]– Meaning: They were worshippers of Allaah and not worshippers of others; and they worshipped Allaah through acts of worship of the heart [i.e. such as love, fear, hope, reliance upon Allaah etc], statements [i.e. all acts of worship uttered by the tongue] and actions [i.e. deeds of the limbs]. [Ref 4]

Allaah [The Most High] said:

وَٱذۡكُرۡ فِى ٱلۡكِتَـٰبِ إِسۡمَـٰعِيلَ‌ۚ إِنَّهُ ۥ كَانَ صَادِقَ ٱلۡوَعۡدِ وَكَانَ رَسُولاً۬ نَّبِيًّ۬ا

وَكَانَ يَأۡمُرُ أَهۡلَهُ ۥ بِٱلصَّلَوٰةِ وَٱلزَّكَوٰةِ وَكَانَ عِندَ رَبِّهِۦ مَرۡضِيًّ۬ا

And mention in the Book [the Qur’an] Ismaa’eel [Ishmael]. Verily! He was true to what he promised, and he was a Messenger, [and] a Prophet. And he used to enjoin on his family and his people As-Salat [the prayers] and the Zakat, and his Lord was pleased with him. [Surah Maryam. Aayaat 54-55]

[وَكَانَ يَأۡمُرُ أَهۡلَهُ ۥ بِٱلصَّلَوٰةِ وَٱلزَّكَوٰةِ وَكَانَ عِندَ رَبِّهِۦ مَرۡضِيًّ۬ا – And he used to enjoin on his family and his people As-Salat [the prayers] and the Zakat, and his Lord was pleased with him]- Meaning: He used to enjoin Allaah’s command on his family – used to command them to establish the prayer which necessitates sincerity and servitude to Allaah, and he used to command them to give Zakaat which necessitates kind treatment towards the slaves of Allaah. So, he [i.e. Ismaa’eel (alayhis salaam)] perfected   himself and others, especially his family – the closest people to him – because they are more worthy of his call [i.e. the guidance he called to] than others. [5]

[1: Source: Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan. (paraphrased)]

[2: Badaa’i-u At-Tafseer Al-Jaami Limaa Fassarahu Al-Imaam Ibnu Qayyim Al-Jawziyyah: vol: 1 page: 125. Slightly paraphrased]

[Ref 3: An Excerpt from ‘Zaarul Maseer Fee Ilmit Tafseer’. By Imaam Ibnul Jawzi (rahimahullaah). Slightly paraphrased]

[Ref 4: An Excerpt from ‘Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan’ by Imaam As-Sadi (rahimahullaah). Slightly paraphrased]

[5: Source: An Excerpt from ‘Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan’. slightly paraphrased