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:3:157 –

And if you are killed in the cause of Allah or die - then forgiveness from Allah and mercy are better than whatever they accumulate ˹in this world˺.  

And if (wa-la-in, the lām is for oaths) you are slain in God’s way, in ˹holy˺ struggle, or die (read muttum or mittum, from ˹singular form˺ māta, yamūtu), that is, if death comes to you thereat, forgiveness, that is, from God, for your sins, and mercy, therefor from Him for you (the clause introduced by the lām ˹of lamaghfiratun, ‘forgiveness’˺ is the response to the oath ˹clause of la’in˺, and occupies the place of the verbal action as a subject, the predicate of which ˹is what follows˺) are better than what they amass, in this world (read tajma‘ūn, ‘you amass’, or yajma‘ūn, ‘they amass’).
القرآن:٣:١٥٧ –

وَلَئِنْ قُتِلْتُمْ فِي سَبِيلِ اللَّهِ أَوْ مُتُّمْ لَمَغْفِرَةٌ مِنَ اللَّهِ وَرَحْمَةٌ خَيْرٌ مِمَّا يَجْمَعُونَ  

{ولئن} لام قسم {قُتِلْتُمْ في سبيل الله} أي الجهاد {أو مُتُّمْ} بضم الميم وكسرها من مات يموت أي أتاكم الموت فيه {لمغفرة} كائنة {من الله} لذنوبكم {ورحمة} منه لكم على ذلك واللام ومدخولها جواب القسم وهو في موضوع الفعل مبتدأ خبره {خير مما تجمعون} من الدنيا بالتاء والياء.