Allah, the Most High, said:
رياض الصالحينAbū Zakariyyā Muḥyī al-Dīn Yaḥyā ibn Sharaf al-Nawawī٨٨ - باب استحباب طيب الكلام وطلاقة الوجه عند اللقاء
٨٨ - باب استحباب طيب الكلام وطلاقة الوجه عند اللقاء
Do not extend your eyes toward that by which We have given enjoyment to [certain] categories of them [i.e., the disbelievers], and do not grieve over them. And lower your wing [i.e., show kindness] to the believers.
And He, the Most High, also said:
فَبِمَا رَحْمَةٍ مِّنَ ٱللَّهِ لِنتَ لَهُمْ ۖ وَلَوْ كُنتَ فَظًّا غَلِيظَ ٱلْقَلْبِ لَٱنفَضُّوا۟ مِنْ حَوْلِكَ ۖ فَٱعْفُ عَنْهُمْ وَٱسْتَغْفِرْ لَهُمْ وَشَاوِرْهُمْ فِى ٱلْأَمْرِ ۖ فَإِذَا عَزَمْتَ فَتَوَكَّلْ عَلَى ٱللَّهِ ۚ إِنَّ ٱللَّهَ يُحِبُّ ٱلْمُتَوَكِّلِينَ
So by mercy from Allāh, [O Muḥammad], you were lenient with them. And if you had been rude [in speech] and harsh in heart, they would have disbanded from about you. So pardon them and ask forgiveness for them and consult them in the matter. And when you have decided, then rely upon Allāh. Indeed, Allāh loves those who rely [upon Him].
وعن عدي بن حاتمٍ - ﵁ - قَالَ: قَالَ رسول الله - ﷺ: «اتَّقُوا النَّارَ وَلَوْ بِشِقِّ تَمْرَةٍ، فَمَنْ لَمْ يَجِدْ فَبِكَلِمَةٍ طَيِّبَةٍ». متفقٌ عَلَيْهِ.
And on the authority of ʿAdī ibn Ḥātim (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings be upon him) said: «Guard yourselves against the Fire, even with half a date; and whoever does not find [even] that, then with a good word.» Agreed upon.
وعن أَبي هريرة - ﵁: أنَّ النبيَّ - ﷺ - قَالَ: «وَالكَلِمَةُ الطَّيِّبَةُ صَدَقَةٌ». متفقٌ عَلَيْهِ، وَهُوَ بعض حديث تقدم بطولِه.
And on the authority of Abū Hurayrah (may Allah be pleased with him): that the Prophet (peace and blessings be upon him) said: «And a good word is a charity.» Agreed upon; and it is part of a ḥadīth already mentioned in full.
وعن أَبي ذَرٍّ - ﵁ - قَالَ: قَالَ لي رسول الله - ﷺ: «لاَ تَحْقِرَنَّ مِنَ الْمَعْرُوفِ شَيْئًا، وَلَوْ أَنْ تَلْقَى أخَاكَ بوَجْهٍ طَلْقٍ». رواه مسلم .
And on the authority of Abū Dharr (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings be upon him) said to me: «Do not belittle any act of kindness, even that you meet your brother with a cheerful face.» Narrated by Muslim.