Smile :)

The Prophet (SAAW) said:

( لا تحقرن من المعروف شيئا ولو أن تلقى أخاك بوجه طلق )
“Do not think little of any act of kindness, even if it is greeting your brother with a cheerful countenance”

And He (SAAW) said :
 ( تبسمك في وجه أخيك صدقة )
“Your smiling at your brother is an act of charity”
And Jarir bin 'Abdullah, may Allah be pleased with him, said: 

(ما حجبني رسول الله صلى الله عليه وسلم منذ أسلمت . ولا رآني إلا تبسم)

Allah's Messenger (may peace be upon him) never refused to give me permission to see him since I embraced Islam and never looked at me but with a smile.