prayer-session: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/prayer-session - from package: prayer

You may install the required package with command apt-get install {package}

Error in other languages:
prayer-session: bevel nie gevind nie
prayer-session: comandă negăsită
prayer-session: comando não encontrado
prayer-session: commande introuvable
prayer-session: command not found
prayer-session: käsku ei ole
prayer-session: không tìm thấy lệnh
prayer-session: komanda nerasta
prayer-session: Kommando nicht gefunden.
prayer-session: kommandot finns inte
prayer-session: komut yok
prayer-session: nie znaleziono polecenia
prayer-session: níor aimsíodh an t-ordú
prayer-session: no se encontró la orden
prayer-session: no s'ha trobat l'ordre
prayer-session: opdracht niet gevonden
prayer-session: parancs nem található
prayer-session: perintah tidak ditemukan
prayer-session: príkaz nenájdený
prayer-session: příkaz nenalezen
prayer-session: команда не найдена
prayer-session: командата не е открита
prayer-session: 命令找不到
prayer-session: コマンドが見つかりません