Sheikh Al-Islam Ibn Taymiyyah said:
“The believers are continually tested [by trials] to purify their imaan and to expiate their sins. This is because the believer performs his actions for the sake of Allah, so it is [incumbent] upon Allah to reward him for that harm which he endured.”
Majmoo’ il Fataawah Vol 18/291-305
لَّيۡسَ ٱلۡبِرَّ أَن تُوَلُّواْ وُجُوهَكُمۡ قِبَلَ ٱلۡمَشۡرِقِ وَٱلۡمَغۡرِبِ وَلَـٰكِنَّ ٱلۡبِرَّ مَنۡ ءَامَنَ بِٱللَّهِ وَٱلۡيَوۡمِ ٱلۡأَخِرِ وَٱلۡمَلَـٰٓٮِٕڪَةِ وَٱلۡكِتَـٰبِ وَٱلنَّبِيِّـۧنَ وَءَاتَى ٱلۡمَالَ عَلَىٰ حُبِّهِۦ ذَوِى ٱلۡقُرۡبَىٰ وَٱلۡيَتَـٰمَىٰ وَٱلۡمَسَـٰكِينَ وَٱبۡنَ ٱلسَّبِيلِ وَٱلسَّآٮِٕلِينَ وَفِى ٱلرِّقَابِ وَأَقَامَ ٱلصَّلَوٰةَ وَءَاتَى ٱلزَّڪَوٰةَ وَٱلۡمُوفُونَ بِعَهۡدِهِمۡ إِذَا عَـٰهَدُواْۖ وَٱلصَّـٰبِرِينَ فِى ٱلۡبَأۡسَآءِ وَٱلضَّرَّآءِ وَحِينَ ٱلۡبَأۡسِۗ أُوْلَـٰٓٮِٕكَ ٱلَّذِينَ صَدَقُواْۖ وَأُوْلَـٰٓٮِٕكَ هُمُ ٱلۡمُتَّقُونَ
It is not Al-Birr (piety, righteousness, and each and every act of obedience to Allâh, etc.) that you turn your faces towards east and (or) west (in prayers); but Al-Birr is (the quality of) the one who believes in Allâh, the Last Day, the Angels, the Book, the Prophets and gives his wealth, in spite of love for it, to the kinsfolk, to the orphans, and to Al-Masâkin (the poor), and to the wayfarer, and to those who ask, and to set slaves free, performs As-Salât (the prayer), and gives the Zakât, and who fulfill their covenant when they make it, and who are patient in extreme poverty and ailment (disease) and at the time of fighting (during the battles). Such are the people of the truth and they are Al¬Muttaqûn
[Al Baqarah (2):177)]
Shaykh Muhammad ibn Saalih al-‘Uthaymeen said:
Among the things we learn from this verse is that what is mentioned is true sincerity towards Allah and towards His creation, because Allah says: “Such are the people of the truth”; they are sincere towards Allah, as on the basis of these good beliefs they establish faith and belief in Allah, the Last Day, the Angels, the Book and the Prophets, and they establish prayer, pay zakaah, and give what is dear to them to the charitable causes mentioned. As for their sincerity towards Allah’s creation, that is included in the words of Allah: “who fulfil their covenant when they make it”, which is one of the signs of sincerity. Hence Allah says: “Such are the people of the truth”, as they are sincere in their beliefs, in their interactions with Allah and with other people.
Tafseer Soorat al-Baqarah, 2/293, 294
Ibn al-Qayyim said:
If a person is sincere towards Allah in all his affairs, Allah will give him more than He gives to others, and this sincerity results from true love of Allah and true trust in Him. So the most sincere of people is the one who loves Allah most and puts the most trust in Him.
Al-Fawaa’id, p 187