Sunan Abu Dawud
4910
Sahih+3

Anas b. Malik reported the Messenger of Allah (May peace be upon him) as saying:Do not hate each other; do not envy each other; do not desert each other; and be the servants of Allah as brethren. It is not allowed for a Muslim to keep apart from his brother for more than three days

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid