Answered by Mawlana Ilyas Patel
Is there a Significance to the forty days after the death of a deceased?
In the Name of Allah, the Most Merciful and Compassionate
There is no significance in the first forty days mentioned in the Quran and hadith. However, the immediate family should mourn for three days.
The Prophet (Allah bless him and give him peace) said, “No one should mourn the death of a person but for three days.” [Bukhari]
Significance of Forty
Remaining and going into the deceased house for forty days in some parts of the Muslim world is a custom. However, if there is no specific religious intention of sunna behind it, then it would be permissible, as it was practiced by some, as mentioned in the following non-Prophetic report (athar)
Imam Ta’us said, “The deceased will get tested by Allah for seven days. For that, they should (who are still alive) arrange feeding on their behalf during those days.” Ubaid bin Umair said, “A believer and a hypocrite will face test together in the grave. For a believer, he will get tested for seven days, while a hypocrite will get tested for forty.”
Ta’us said, “Indeed people who have died are tested in the grave for seven days, then they (the companions of the Prophet) loved to arrange to feed on their behalf.” [Adam al Atyubi Dhakhiratul-Uqba fi Sharh al-Mujtaba; Al Suyuti, Al Hawi lil Fatawa]
Various Practices of Gathering for Days
It is possible due to the above non-prophetic report (athar) mentioned in many books – although the forty is about a Hypocrite – some companions fed others on behalf of the deceased. Maybe, this is why one sees varied practices and ways of donating rewards for the dead, and gatherings take place for this purpose.
Here is a link for further understanding:
Is It Permissible to Gather for Reciting Quran for the Deceased? (seekersguidance.org)
I want to recommend you the following reading:
The soul’s journey after death
I hope this helps.
[Mawlana] Ilyas Patel
Checked and Approved by Shaykh Faraz Rabbani