Aswad bin Yazid says that once the prayer had been established in the mosque, we were going to join the rows with Sayyiduna Ibn Mas'ud (may Allah be pleased with him). When the people went into bowing (ruku'), Sayyiduna Ibn Mas'ud (may Allah be pleased with him) also went into ruku', and seeing him, we too performed ruku' while we were still walking. During this, a man passed by from the front and said: "As-salamu 'alayka ya Aba 'Abd al-Rahman!" In the state of ruku', he replied: "Allah and His Messenger have spoken the truth." After the prayer, someone asked him, "When that person greeted you, why did you say that Allah and His Messenger have spoken the truth?" He replied, "I heard the Prophet (peace and blessings be upon him) say: 'It is among the signs of the Hour that greeting (salam) will be given only to those who are known.'"