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
suyuti:1305a –

the Messenger of Allah ﷺ said: “When you give Zakat, do not forget its reward, and say 'Allahummaj-'alha maghnaman wa la taj-'alha maghrama (O Allah! Make it a gain and do not make it a loss).' ” (Maudu') (Using translation from Ibn Mājah 1797)   

السيوطي:١٣٠٥a –

"إِذَا أَعْطِيتُم الزّكاةَ فلا تَنسَوْا ثوَابَها- أن تقولُوا: اللهم اجْعلها مغْنمًا ولا تجعلها مغرمًا" .  

[هـ] ابن ماجة [ع] أبو يعلى [كر] ابن عساكر في تاريخه عن أبي هريرة وضعف

See similar narrations below:

Collected by Ibn Mājah
ibnmajah:1797 – Sūwayd b. Saʿīd > al-Walīd b. Muslim > al-Bakhtarī b. ʿUbayd from his father > Abū Hurayrah

the Messenger of Allah ﷺ said: “When you give Zakat, do not forget its reward, and say 'Allahummaj-'alha maghnaman wa la taj-'alha maghrama (O Allah! Make it a gain and do not make it a loss).' ” (Maudu')  

ابن ماجة:١٧٩٧ – حَدَّثَنَا سُوَيْدُ بْنُ سَعِيدٍ حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ عَنِ الْبَخْتَرِيِّ بْنِ عُبَيْدٍ عَنْ أَبِيهِ عَنْ أَبِي هُرَيْرَةَ قَالَ

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا أَعْطَيْتُمُ الزَّكَاةَ فَلاَ تَنْسَوْا ثَوَابَهَا أَنْ تَقُولُوا اللَّهُمَّ اجْعَلْهَا مَغْنَمًا وَلاَ تَجْعَلْهَا مَغْرَمًا