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:3919a –

that the Prophet ﷺ said: "Recite the Qur'an in forty (days)." (Using translation from Tirmidhī 2947)   

السيوطي:٣٩١٩a –

"اقرأ القرآن في أرْبَعينَ ".  

[ت] الترمذي حسن غريب عن ابن عمرو

See similar narrations below:

Collected by Tirmidhī, Suyūṭī
tirmidhi:2947 – Abū Bakr b. Abū al-Naḍr al-Baghdādī > ʿAlī b. al-Ḥasan > Ibn Shaqīq > ʿAbdullāh b. al-Mubārak > Maʿmar > Simāk b. al-Faḍl > Wahbb. Munabbih > ʿAbdullāh b. ʿAmr

that the Prophet ﷺ said: "Recite the Qur'an in forty (days)."  

الترمذي:٢٩٤٧ – حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي النَّضْرِ الْبَغْدَادِيُّ قَالَ حَدَّثَنَا عَلِيُّ بْنُ الْحَسَنِ هُوَ ابْنُ شَقِيقٍ عَنْ عَبْدِ اللَّهِ بْنِ الْمُبَارَكِ عَنْ مَعْمَرٍ عَنْ سِمَاكِ بْنِ الْفَضْلِ عَنْ وَهْبِ بْنِ مُنَبِّهٍ عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو

أَنَّ النَّبِيَّ ﷺ قَالَ لَهُ اقْرَإِ الْقُرْآنَ فِي أَرْبَعِينَ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ وَ قَدْ رَوَى بَعْضُهُمْ عَنْ مَعْمَرٍ عَنْ سِمَاكِ بْنِ الْفَضْلِ عَنْ وَهْبِ بْنِ مُنَبِّهٍ أَنَّ النَّبِيَّ ﷺ أَمَرَ عَبْدَ اللَّهِ بْنَ عَمْرٍو أَنْ يَقْرَأَ الْقُرْآنَ فِي أَرْبَعِينَ