Hadith: When you hear the Muezzin, say what he says and then invoke Allah's blessings upon me

عَنْ ‌عَبْدِ اللهِ بْنِ عَمْرِو بْنِ الْعَاصِ رضي الله عنها أَنَّهُ سَمِعَ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يَقُولُ:
«إِذَا سَمِعْتُمُ الْمُؤَذِّنَ فَقُولُوا مِثْلَ مَا يَقُولُ، ثُمَّ صَلُّوا عَلَيَّ، فَإِنَّهُ مَنْ صَلَّى عَلَيَّ صَلَاةً صَلَّى اللهُ عَلَيْهِ بِهَا عَشْرًا، ثُمَّ سَلُوا اللهَ لِيَ الْوَسِيلَةَ، فَإِنَّهَا مَنْزِلَةٌ فِي الْجَنَّةِ، لَا تَنْبَغِي إِلَّا لِعَبْدٍ مِنْ عِبَادِ اللهِ، وَأَرْجُو أَنْ أَكُونَ أَنَا هُوَ، فَمَنْ سَأَلَ لِيَ الْوَسِيلَةَ حَلَّتْ لَهُ الشَّفَاعَةُ».
[صحيح] - [رواه مسلم] - [صحيح مسلم: 384]

‘Abdullāh ibn ‘Amr ibn al-‘Ās (may Allah be pleased with him) reported that he heard the Prophet (may Allah’s peace and blessings be upon him) say:
"When you hear the Muezzin, say what he says and then invoke Allah's blessings upon me, for whoever invokes Allah's blessings upon me once, Allah will bestow His blessings upon him ten times. Then, ask Allah to grant me the Wasīlah, a high rank in Paradise that befits only one of Allah's servants, and I hope that I will be him. If anyone asks for Wasīlah for me , intercession will be permitted for him.”
[Authentic hadith] - [Narrated by Muslim] - [Sahih Muslim - 384]

Explanation

The Prophet (may Allah's peace and blessings be upon him) instructed those who hear the Muezzin making the call to prayer to repeat after him and say as he says, except for "hayy' ala as-salāh" (come to prayer) and "hayy 'ala al-falāh" (come to success), after which they should say: "lā hawla wa la quwwata illa billāh" (there is no power nor strength except through Allah). Then, after the end of the Adhān, they should invoke Allah's blessings upon the Prophet (may Allah's peace and blessings be upon him), for whoever invokes Allah's blessings upon him once, Allah will bestow His blessings upon him ten times on account of it. The meaning of Allah's bestowal of blessings upon a servant is that He praises him before the angels.
Then, he (may Allah's peace and blessings be upon him) commanded that we ask Allah to grant him the Wasīlah, the highest rank in Paradise. It does not befit and will not be given except to one person from among Allah Almighty's servants, and I hope it will be me. The Prophet (may Allah's peace and blessings be upon him) said that out of modesty, for if this rank can only be given to one person, that one person could only be him (may Allah's peace and blessings be upon him), for he is the best among all mankind.
Then, he (may Allah's peace and blessings be upon him) pointed out that whoever supplicates Allah to give the Wasīlah to the Prophet (may Allah's peace and blessings be upon him) will gain the Prophet's intercession.