What to say when you hear the call of prayer
The call of prayer (Adhan) is the announcement of the time for the obligatory prayer through a specific phrase, and the Holy Quran and Prophetic Sunnah indicate the legitimacy of the call of prayer. The call of prayer (Adhan) has been mentioned twice in the Holy Quran, the first time, Adhan is mentioned in general in Aya (58) of Surat Alma'idah {And when you call to the prayer, they take it in ridicule and play, that is because they are a people who do not understand}. The call of prayer is mentioned a second time, but specifically for Friday prayer in Aya (9) of Surat Aljumu'ah {O you who believed! When the call is made for prayer on Friday, then Proceed to the remembrance of Allah, and leave trade, that is better for you if you only know}.
And as narrated by Malik bin Huwairth: "I came to the Prophet (PBUH) with some men from my tribe and stayed with Him for twenty nights, He was kind and merciful to us, when He realized our longing for our families, He said to us Go back and Stay with with your families and Teach them the religion, and Offer the prayer, and one of you should pronounce the Adhan for the prayer when its time is due, and the oldest one amongst you should lead the prayer" (Sahih Albukhari 628).
The wording of the Adhan
Umar bin Alkhattab, May Allah be pleased with him, was the first to suggest that the call to prayer be pronounced when Muslims disagreed on how to gather for prayer, but the wording of Adhan came from a dream seen by a man from the Ansar named Abdullah bin Zaid, and Umar bin Alkhattab also had the same dream, as Abdullah bin Umar narrated: "When the Muslims arrived at Medina, they used to assemble for the prayer and used to guess the time for it, during these days, the practice of Adhan for the prayer had not been introduced yet. Once they discussed this problem regarding the call for prayer, some people suggested the use of a bell like the Christians, other proposed a trumpet like the horn used by the Jews, but Umar was the first to suggest that a man should call for the prayer, so Allah's Messenger (PBUH) ordered Bilal to get up and pronounce the call for prayer" (Sahih Albukhari 604).
And Abdullah bin Zaid reported: "When the Messenger of Allah (PBUH) ordered a bell to be made so that it might be struck to gather the people for prayer, a man carrying a bell in his hand appeared to me while I was asleep, and I said servant of Allah! Will you sell the bell?, he asked What will you do with it?, I replied we shall use it to call the people to prayer. He said Should I not suggest you something better than that, I replied certainly, then he told me to say Allahu Akbaru Allahu Akbar, Allahu Akbaru Allahu Akbar (Allah is the Greatest), Ashhadu an la ilaha illa Allah, Ashhadu an la ilaha illa Allah (I bear witness that there is no God but Allah), Ashhadu anna Muhammadan rasulu Allah, Ashhadu anna Muhammadan rasulu Allah (I bear witness that Muhammad is the Messenger of Allah), Hayya ala alsalah, Hayya ala aslsalah (Come to the prayer), Hayya ala alfalah, Hayya ala alfalah (Come to the Success), Allahu Akbaru Allahu Akbar (Allah is the Greatest), La ilaha illa Allah (There is no God but Allah). He then moved backward a few steps and said when you utter the Iqamah, you should say Allahu Akbaru Allahu Akbar (Allah is the Greatest), Ashhadu an la ilaha illa Allah, Ashhadu an la ilaha illa Allah (I bear witness that there is no God but Allah), Ashhadu anna Muhammadan rasulu Allah (I bear witness that Muhammad is the Messenger of Allah), Hayya ala aslsalah (Come to the prayer), Hayya ala alfalah (Come to the Success), qad qamati alsalah, qad qamati alsalah (The time for prayer has come), Allahu Akbaru Allahu Akbar (Allah is the Greatest), La ilaha illa Allah (There is no God but Allah).
Abdullah bin Zaid added, when the morning came, I came to the Messenger of Allah (PBUH) and informed Him of what I had seen in the dream, He said it is a true vision, if Allah wills, so Go with Bilal and Tell him what you had seen, so that he may call to prayer with it, for he has a louder voice than you have. so I got up along with Bilal and began to teach it to him and he used it in making the call to prayer. Umar bin Alkhattab, May Allah be pleased with him, heard it while he was in his house, and came out dragging his clock and said Messenger of Allah! By the One who has sent you with the truth, I have also seen the same thing that he saw. The Messenger of Allah said Praise be to Allah" (Sunan Abi Dawood 499).
The Messenger of Allah (PBUH) commanded that the phrase Alsalatu khairun mena alnawm: the prayer is better than sleep, be said twice in the Fajr prayer before the last two phrases of the Adhan, as Abu Mahdhurah said that the Messenger of Allah taught him the Adhan and said to him: "If it is the morning prayer (Fajr), you must pronounce Alsalatu khairun mena alnawm, Alsalatu khairun mena alnawm: the prayer is better than sleep, Allahu Akbaru Allahu Akbar (Allah is the Greatest), La ilaha illa Allah (There is no God but Allah" (Sunan Abi Dawood 500).
What to say when hearing the Adhan
Allah's Messenger (PBUH) said in narration of Abu Sa'id Alkhudri: "Whenever you hear the Adhan, Say what the Mu'adhdhin (The caller of prayer) is saying" (Sahih Albukhari 611). And Allah's Messenger used to say La hawla wa la quwwata ella bellah: There is neither might nor power except by Allah when the Mu'adhdhin says Hayya ala alsalah and Hayya ala alfalah, as Yahya reported: "Some of my companions told me that Hisham had said when the Mu'adhdhin (Caller of prayer) said Hayya al alsalah Mu'awiya said La hawla wa la quwwata ella bellah: There is neither might nor power except by Allah, and added we heard your Prophet (PBUH) saying the same" (Sahih Albukhari 613).
And Umar bin Alkhattab narrated: "The Messenger of Allah (PBUH) said when the Mu'adhdhin says Allahu Akbaru Allahu Akbar, and one of you should say Allahu Akbaru Allahu Akbar, then the Mu'adhdhin says Ashhadu an la ilaha illa Allah, and he says Ashhadu an la ilaha illa Allah, the Mu'adhdhin says Ashhadu anna Muhammadan rasulu Allah, and he says Ashhadu anna Muhammadan rasulu Allah, the Mu'adhdhin says Hayya ala alsalah, he says la hawla wala quwwata illa billah, then the Mu'adhdhin says hayya ala alfalah, he says la hawla wala quwwata illa billah, he will enter Paradise if he makes this response from his heart" (Sahih Muslim 385).
What to say after hearing Adhan
The prophet (PBUH) said in narration of Jabir bin Abdullah: "Whoever after hearing the Adhan says Allahumma Rabba hazehi alda'wati altammah, wa alsalati alqa'imah, ati Muhammadan al-wasilata wa al-fadilah, wa b'thuhu maqaman mahmudan allazi wa'adtahu: O Allah! Lord of this perfect call, and this prayer which is going to be established, Give Muhammad the right of intercession and eminence and Resurrect Him to the best and the highest place in Paradise that You promised Him, then My intercession for him will be allowed on the day of resurrection" (Sahih Albukhari 614).
And Sa'd Bin Abi Waqqas narrated that the Messenger of Allah (PBUH) said: "If anyone says on hearing the Mu'adhdhin ashhadu an la ilaha illa Allahu wahdahu la sharika lahu, wa anna Muhammadan abduhu wa rasuluhu, radaitu be-llahi Rabban, wa be-muhammadin rasulan wa bel-islami deena: I bear witness that there is no God but Allah, Alone, with no partner, and that Muhammad is His Servant and His Messenger. I am satisfied with Allah as my Lord, with Muhammad as Messenger, and with Islam as religion, his sins will be forgiven" (Sahih Muslim 386).