The established Prophetic traditions.
Supplicating for fellow Muslims in their absence.
On the authority of Abu al-Darda' (may Allah be pleased with him),
that he heard the Messenger of Allah (peace and blessings of Allah be upon him) say:
"Whoever supplicates for his brother in his absence,
the angel appointed over him says,
'Ameen,
and may you be granted the like thereof.'"
Narrated by Muslim.