When one Muslim meets another he should confront him with a smile and cheerful countenance and physically express his delight in meeting him. This will entail a fortification of love and affection between them. If you confront a grieved person with a cheerful countenance, you might just allay his grief or at least pacify him. A person feels unrestrained in expressing himself if he is confronted cheerfully thereby aiding him in fulfilling his needs.

Hadhrat Abu Dhar (رضى الله تعالى عنه) narrates that the Holy Prophet (صلى الله عليه وسلم) said:
“Don’t ever belittle any of your good deeds even though this may be meeting your brother with a cheerful countenance.” [Muslim]

The Holy Prophet (صلى الله عليه وسلم) said:
“When two Muslims meets and clasp each others hands, their sins are shed as a tree sheds it’s leaves.”

Together with a buoyant confrontation, clasping each others hands is also mustahab (preferable) as this increases mutual love and affection.

Hadhrat Qatadah (رضى الله تعالى عنه) relates that he enquired of Hadhrat Anas (رضى الله تعالى عنه) if the companions of the Holy Prophet (صلى الله عليه وسلم) grasped each others hands whilst meeting. Hadhrat Anas (رضى الله تعالى عنه) replied: “Yes of course!” [Fathul Baari]

Hadhrat Baraa (رضى الله تعالى عنه) narrates that the Holy Prophet (صلى الله عليه وسلم) said:
“When two Muslims meet one another and clasp each others hands, they are forgiven even before they separate from one another.” [Abu Daud]

Source: The 40 Pathways to Jannah by Sheikh Khalid Sayyid Ali