What are hadiths about sincerity? Examples of hadiths about sincerity…
According to Umama al-Bahiliyya (ra), the Messenger of Allah (saw) said, “Allah does not accept any deed, except that which is purely for Him, and seeking His sake.” (al-Nasaʾi, al-Jihad, 24)
According to Tamim al-Dariyya (ra), the Messenger of Allah (saw) stated, “Al-Dīn (religion) is sincerity and well wishing.” Thereupon we said, “For whom?” He replied, “For Allah, His Book, His Messenger and for the leaders of Muslims and Muslims in general.” (Muslim, al-Iman, 95)
Zayd b. Arqam (ra) reported that the Prophet (saw) supplicated after the prayer in congregation as follows: “O Allah, our Lord and Lord of everything, I bear witness that You are the Lord alone Who has no partner; O Allah, our Lord and Lord of everything, make me sincere to You, and my family as well at every moment, in this world and in the world of the Hereafter.” (Abu Daʾud, al-Witr, 25)
According to Abu Hurayra (ra), the Prophet (saw) said, “Verily, Allah does not look at your physical appearances and your wealth but He looks at your hearts and your deeds.” (Muslim, al-Birr, 34)
According to Anas b. Malik (ra), the Messenger of Allah (saw) said, “Whosoever departs this world with sincerity towards Allah, worshipping Him alone with no partner, establishing regular prayer and paying zakāt, he dies while Allah is pleased with him.” (Ibn Maja, al-Sunna, 9)
Source: Presidency Of Religious Affairs The Turkey, Islam Through Hadiths