Sahih Bukhari Volume 1, Book 10, Hadith 616

حَدَّثَنَا مُسَدَّدٌ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ أَيُّوبَ، وَعَبْدِ الْحَمِيدِ، صَاحِبِ الزِّيَادِيِّ وَعَاصِمٍ الأَحْوَلِ عَنْ عَبْدِ اللَّهِ بْنِ الْحَارِثِ قَالَ خَطَبَنَا ابْنُ عَبَّاسٍ فِي يَوْمٍ رَدْغٍ، فَلَمَّا بَلَغَ الْمُؤَذِّنُ حَىَّ عَلَى الصَّلاَةِ‏.‏ فَأَمَرَهُ أَنْ يُنَادِيَ الصَّلاَةُ فِي الرِّحَالِ‏.‏ فَنَظَرَ الْقَوْمُ بَعْضُهُمْ إِلَى بَعْضٍ فَقَالَ فَعَلَ هَذَا مَنْ هُوَ خَيْرٌ مِنْهُ وَإِنَّهَا عَزْمَةٌ‏

Narrated By 'Abdullah bin Al-Harith : Once on a rainy muddy day, Ibn 'Abbas delivered a sermon in our presence and when the Mu'adhdhin pronounced the Adhan and said, "Haiya ala-s-sala(t) (come for the prayer)" Ibn 'Abbas ordered him to say 'Pray at your homes.' The people began to look at each other (surprisingly). Ibn 'Abbas said. "It was done by one who was much better than I (i.e. the Prophet or his Mu'adhdhin), and it is a license.'