It has been related by Al-Miqdaam bin Ma’di Karib that the Prophet (peace be upon him) said:
“If any of you loves his brother then he should inform him”
(Tirmidhi, Hadeeth Hasan Sahih)
Also it was narrated from Anas ibn Maalik (may Allaah be pleased with him) that a man was with the Prophet (peace and blessings of Allaah be upon him) when another man passed by and he said:
O Messenger of Allaah, I love this man.
The Prophet (peace and blessings of Allaah be upon him) said to him: “Have you told him?”
He said: No.
He said: “Tell him.”
So he caught up with him and said: I love you for the sake of Allaah.
He said: May the one for Whose sake you love me also love you.
Related by Imam Ahmad and Abu Daawood and it is hadeeth sahih and classed as saheeh by al-Nawawi in Riyadh al-Saaliheen (183) and classed as hasan by al-Albaani in Saheeh Abi Dawood).
In some reports of the hadeeth it says: “Tell him for it will strengthen the love between you.”
Narrated by Ibn Abi’l-Dunya in al-Ikhwaan (69)