Sunan Abu Dawud
2862
Sahih+3

Narrated 'Abdullah bin 'Umar:The Messenger of Allah (ﷺ) as saying: It is the duty of a Muslim man who has something which is to be given as bequest not to have it for two nights without having his will written regarding it

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid