Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: I saw the Messenger of Allah (peace and blessings be upon him); he would say the takbir when rising and when sitting, and he would give the salam to his right and to his left, until I could see the whiteness of his blessed cheek on both sides. And I saw Abu Bakr and Umar (may Allah be pleased with them both); they too did the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2975