All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is recommended to supplicate Allaah for the deceased at any time for the verse (what means): {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."} [Quran 59:10 ] We do not know an affirmed supplication to be cited while washing or shrouding the deceased. Also, there is no determined number for those who prepare the deceased. However, some jurists stated that it should be an odd number.
The Shaafi‘i scholar Zakariyyaa Al-Ansaari said: "The number of those who wash or bury the deceased is recommended to be an odd number; three or more as needed."
Allaah Knows best.