Abdullah bin Masud said, "Whoever follows a funeral procession should carry all four sides of the bier, for that is from the Sunnah. After that, if he wishes he may continue voluntarily, and if he wishes he may leave it."
حدثنا حميد بن مسعدة حدثنا حماد بن زيد عن منصور عن عبيد بن نسطاس
قال عبد الله بن مسعود من اتبع جنازة فليحمل بجوانب السرير كلها فإنه من السنة ثم إن شاء فليتطوع وإن شاء فليدع
No references are available.
[Its chain of transmission is daif due to a break in it.] Busiri said, "It is disconnected, for Abu Ubayda did not hear from his father." This was stated by Abu Hatim, Abu Zura, and others. See hadith no. 1606.