Imam Jafar Sadiq (a.s.): When the name of the Prophet is mentioned in your presence you must invoke excessive blessings on him, because one who invokes blessings on him once, Allah blesses him a thousand times. And nothing created by Allah is such that it does not follow suit. One who refrains from this is arrogant and Allah, the Prophet (s.a.w.a.) and Ahle Bait (a.s.) are aloof from him.
Hayaat al-Quloob v 2 chap 10