Short answer
Nothing special is set by the Quran or sunnah for the 40th day, or the 3rd, 7th or 10th. Hanafi scholars of the Deobandi tradition hold that fixing these days for gatherings and meals as a religious practice has no basis. Making dua, reciting Quran and giving charity for the dead is good on any day.
Gifting reward to the dead is good at any time. Making a specific day such as the 3rd, 10th or 40th a religious occasion, with set gatherings and food prepared by the bereaved family, is an innovation (bid'ah) and makruh. The family hosting a feast for mourners is makruh.
The four schools agree on this.
Explanation
In many cultures, families gather on the third day (soyem or qul), the seventh, the tenth, the fortieth (chehlum or chaliswan) and the yearly anniversary. People often ask whether the soul returns home on these days, or whether something happens to the dead on day 40.
What the sources say. No authentic hadith fixes the 40th day, or any other day, for the dead. There is no sound evidence that the soul visits the home for 40 days. What happens after death belongs to the barzakh, the life between death and resurrection; see barzakh and the afterlife.
The Hanafi position. Hanafi books say it is disliked for the family of the dead to host meals for guests, because feasts are for times of joy, not grief. The sunnah is the reverse: neighbours and relatives cook for the grieving family. Scholars of the Deobandi tradition add that tying good deeds to fixed days and treating them as part of the religion is an innovation, because the Prophet ﷺ said anything added to the religion that is not from it is rejected.
Other views. Some scholars in South Asia, especially in the Barelvi tradition, allow these gatherings as long as people do not believe the day is required and the food is for the poor. AmalKit follows the position above, and it is fine to hold your view kindly with family who see it differently.
What you can do any day:
- Make dua and recite Quran for them; see isal al-thawab.
- Give charity, feed the poor, or fund sadaqah jariyah in their name.
- Pay their debts and keep good ties with their friends and family.
The evidence
Quran, Surah Al-Hashr 59:10
وَٱلَّذِينَ جَآءُو مِنۢ بَعْدِهِمْ يَقُولُونَ رَبَّنَا ٱغْفِرْ لَنَا وَلِإِخْوَٰنِنَا ٱلَّذِينَ سَبَقُونَا بِٱلْإِيمَٰنِ وَلَا تَجْعَلْ فِى قُلُوبِنَا غِلًّۭا لِّلَّذِينَ ءَامَنُوا۟ رَبَّنَآ إِنَّكَ رَءُوفٌۭ رَّحِيمٌ ﴿١٠﴾
And [there is a share for] those who came after them, saying, "Our Lord, forgive us and our brothers who preceded us in faith and put not in our hearts [any] resentment toward those who have believed. Our Lord, indeed You are Kind and Merciful."
Dua for the dead has no fixed day.
Sahih al-Bukhari 2697
Sahih... من أحدث في أمرنا هذا ما ليس فيه فهو رد ...
"Whoever adds to this matter of ours something that is not part of it, it is rejected."
Fixed religious rites need a basis in the sunnah.
Sunan Abi Dawud 3132
Graded hasan... اصنعوا لآل جعفر طعاما فإنه قد أتاهم أمر شغلهم ...
"Make food for the family of Ja'far, for what has come to them keeps them busy."
Others feed the bereaved family, not the other way round.
Where the ruling is recorded
- Fath al-Qadir, Kitab al-Salah, Bab al-Jana'iz. Hosting a meal by the family of the dead is disliked, since feasts are for joy and not grief.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Salah, Bab Salat al-Janazah. The dislike of fixed-day gatherings and meals after death.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.