Imam Muhammad bin Ali narrates from his father the statement of Sayyiduna Ali (may Allah be pleased with him): Jibreel (peace be upon him) descended with the words of Iqamah separately; the Noble Prophet (peace and blessings be upon him) prescribed reciting the words twice in the Adhan as Sunnah.
Hadith Referenceسنن الدارقطني / كتاب الصلاة / 933
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 933، وابن أبى شيبة فى ((مصنفه)) برقم: 2150، والطحاوي فى ((شرح معاني الآثار)) برقم: 836»