Holy Avtar Vani - Shabad No. 259
Satjug andar ese ne hi aa prahlaad bachaya si;
Treta de vich maar ke raavan dwaapar karishan sadaaya si.
Ese ne hi kaljug andar naanak naam rakhaya si;
Ese ne hi roop badal ke boota gyaan da laya si.
Aad ton hai eh aape ikko jisnun jag nirankar kahe;
Bachan guru da hai rab aape baar baar avtar kahe.
Meaning
Here it has been said repeatedly that the Word of the True Master is the word of God himself. In the Golden age (Satyug), God Himself appeared and saved Prahlad; In the Silver age (Treta), He killed Ravana and in the Bronze age (Dwapar) He came to be known as Lord Krishna. In the Iron age (Kalyug), He got Himself named as Nanak; God Himself changed His form and rooted a plant (Buta) of God- Knowledge. Since beginning God is one, whom the world calls the Formless (Nirankar).