It is narrated from Sayyiduna Abdullah bin Malik Ibn Buhaynah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) went out for the morning prayer, and Sayyiduna Bilal (may Allah be pleased with him) was with him (peace and blessings be upon him). He called the iqamah for the prayer, and he (peace and blessings be upon him) passed by me, struck my shoulder and said: "Will you pray four rak'ahs for the morning prayer?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4543