‘Ubaadah ibn As-Saamit, may Allah be pleased with him, reported that he heard the Messenger of Allah, sallallaahu ‘alaihi wa sallam, say: “Whenever a Muslim supplicates to Allah, He accepts his supplication, or averts any affliction from him, or saves its equivalent in reward for him until the Day of Account – as long as he does not supplicate for something that is sinful or something that may break the ties of kinship.” [At-Tirmithi]
Jaabir, may Allah be pleased with him, said: “Some of the residents of Koofah complained to (the Caliph) ‘Umar, may Allah be pleased with him, about (his governor of Iraq) Sa’d, may Allah be pleased with him, claiming that he did not know how to lead his people in prayer properly. In response to this, Sa’d said: ‘I pray in the exact manner I saw the Prophet, sallallaahu ‘alaihi wa sallam, pray. I make the first two Rak’ahs longer than the last two in the Isha prayer’. Upon hearing this, ‘Umar said: ‘This is what I thought your practice would be.’
After that ‘Umar sent some people to Koofah to inquire about the situation. Whenever they entered a mosque and asked the congregation there, they would praise Sa’d. When they reached a mosque where the tribe of Banu ‘Abs lived, one man said: ‘As you have asked us about Sa’d, we will tell you the truth: he is unfair when judging between people and does not justly distribute (war booty) and never participates in battles.’
Upon hearing this, Sa’d supplicated to Allah saying: ‘O Allah! If this man is lying, make him go blind, make him live to an old age and expose him to temptations.’ Some Muslims later narrated that: ‘Indeed we saw this man running after young girls in the streets, harassing them. He would say: ‘Indeed the supplication of Sa’d against me has been realised.’”
Ibn al-Munkadir, may Allah be pleased with him, said: “Once, I was sitting in the mosque next to the pulpit supplicating in the middle of the night. There was a man standing next to one of the pillars of the mosque covering his face with a mask. I overheard him saying whilst supplicating: ‘O my Lord! Drought has severely affected Your slaves, and I adjure You to bring down rain upon us!’ It was not but a short while that a cloud came with rain.”
Ibn al-Munkadir was keen to know all the righteous people and thus decided to try to find out who this man was. He said: “I said to myself: ‘There is a pious man in the city who I do not know’, so when he concluded his prayer, I followed him until he reached the house of Anas, and entered it. I went back, and after I prayed the Fajr prayer I went to his house and knocked his door. When he opened the door, I asked him: ‘I overheard you last night supplicating and I saw what resulted from your supplication. Would you allow me to provide your sustenance so that you can concentrate on your worship?’ He replied: ‘No, but I have a favour to ask of you. Please do not mention what you saw to anyone until I die, and do not come back again, because people would notice and my matter would become publicly known’ I said to him: ‘But where can I meet you?’ He replied: ‘In the mosque’” Ibn al-Munkadir never mentioned what he saw to anyone until the man died.
Ibn Wahb, may Allah be pleased with him,  said: “I was told that the man moved out of the house he was living in to another location which no one knew about, so the owners of the house from whom he was renting the house said: ‘May Allah forgive Ibn al-Munkadir who forced this righteous man to leave our house.’”
‘Abbaas Ad-Doori, may Allah be pleased with him, reported that ‘Ali ibn Abu Fazaarah, may Allah be pleased with him, said: “My mother was handicapped for twenty years. One day she said to me: ‘Go to Ahmad ibn Hanbal and request him to supplicate for me to be cured.’ I went to him, may Allah have mercy upon him, and knocked on his door, so he asked me what my need was. I told him that my mother was requesting that he supplicates for her to be cured. He replied in an angry tone: ‘I am in greater need for someone to supplicate for me.’ As I was about to head back home, an old lady came out and said: ‘He started supplicating for your mother after you had left.’ When I reached home, my mother was at my reception (i.e., Allah had cured her).”
Sulaym ibn ‘Aamir, may Allah be pleased with him, stated: “I entered upon Al-Jarraah (before a battle) and he raised his hands up and started supplicating, and the leaders of the army did likewise, so I did the same. He supplicated for a long time, and then said to me: ‘Do you know what we were doing?’ I said: ‘No, but I saw you supplicating earnestly, so I raised my hands with you.’ He then said: ‘We were supplicating to Allah to grant us martyrdom.’” Sulaym ibn ‘Aamir then said: “I swear by Allah that every single one of them was martyred during this battle.”
Bilaal ibn Ka’b, may Allah be pleased with him, reported that some young men said to Abu Muslim al-Khawlaani, may Allah be pleased with him: “Supplicate to Allah to enable us to catch this antelope.” He supplicated to Allah and they were able to catch it immediately.
Article source: http://www.islamweb.net/emainpage/