“And say to My slaves (i.e. true believers) that they should say (only) those words that are the best.”
(Aayah No. 53, Surah Al-Isra’, Chapter No. 17, Holy Qur’an).
2.2. There is a Hadith also regarding this matter:
Narrated Abu Hurairah (RA): The prophet (PBUH) said, “A good, pleasant, friendly word is a ‘Sadaqa‘.”
(Chapter 34, Book of Al-Adaab, Sahih Bukhari, Vol. 8).