Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:18:104 –

˹They are˺ those whose effort is lost in worldly life, while they think that they are doing well in work."  

Those whose effort goes astray in the life of this world, ˹those˺ whose deeds are invalid, while they reckon, they think, that they are doing good work, ˹good˺ deeds for which they will be rewarded.
القرآن:١٨:١٠٤ –

الَّذِينَ ضَلَّ سَعْيُهُمْ فِي الْحَيَاةِ الدُّنْيَا وَهُمْ يَحْسَبُونَ أَنَّهُمْ يُحْسِنُونَ صُنْعًا  

{الذين ضل سعيهم في الحياة الدنيا} بطل عملهم {وهم يحسبون} يظنون {أنهم يحسنون صنعا} عملاً يجازون عليه.