Sayyiduna Samurah bin Jundub (may Allah be pleased with him) said that the battle-cry of the Muhajirun was "Ya Abdallah!" (O servant of Allah!) and the battle-cry of the Ansar was "Ya Abd al-Rahman!" (O servant of the Most Merciful!).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13052