Sunan Ibn Majah
Sunan Ibn Majah 729
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ الْجَرَّاحِ، حَدَّثَنَا الْمُعْتَمِرُ بْنُ سُلَيْمَانَ، عَنْ خَالِدٍ الْحَذَّاءِ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ الْتَمَسُوا شَيْئًا يُؤْذِنُونَ بِهِ عِلْمًا لِلصَّلاَةِ فَأُمِرَ بِلاَلٌ أَنْ يَشْفَعَ الأَذَانَ وَيُوتِرَ الإِقَامَةَ .
Unreviewed translation. All hadiths in this collection are available in five languages. Titles and introductions may remain in Arabic.
'Abdullah ibn al-Jarrah narrated to us: al-Mu'tamir ibn Sulayman narrated to us, from Khalid al-Hadhdha', from Abu Qilabah, from Anas ibn Malik, who said: They sought a signal by which to announce that the prayer had begun. Bilal was then instructed to pronounce the call with its phrases in pairs and the iqamah with an odd number of phrases.
Notes and open questions — unreviewed
The Arabic describes the adhan as shaf' (paired) and the iqamah as witr (odd-numbered).