One of the Isfahani traders who was well trusted by a group of scholars had a dream about Imam Mahdi. In his dream, he asked Imam when he would return. Imam Mahdi said, “Soon. Tell the Shiites to say the Nodbeh prayer on Fridays.”
The ‘Faraj’ Prayer
Late Sheikh Tabarsi said in his book “Konouz al Najah”, “Abolhasan Muhammad bin Ahmad bin al Lais was afraid of getting killed, so he took refuge next to the graves of Imam Kazem and Imam Javad. He visited Imam Mahdi in a dream. Imam taught him how to say the ‘Faraj’ prayer and because of saying this prayer, the man was saved from getting killed.
Praying for Imam Mahdi to Return Sooner
Mirza Muhammad Baqir Isfahani said that he had a dream about Imam Hassan Mojtaba who told him, “Tell people to repent and to pray for Imam Mahdi to return soon. Saying this prayer is not a choice, but it is mandatory for everyone.”
When Late Ayatollah Hajj Seyyed Muhammad, the son of Ayatollah Seyyed Jamal Al Din Golpayegani met Imam Mahdi, Imam told him, “Only one event is left till my return and that might happen soon. You should pray for me to come to you soon.”
source : http://www.tebyan.net