The Zina (adultery) of the eye is the (lustful) look,
the Zina of the ears is the listening (to voluptuous talk),
the Zina of the tongue is (the licentious) speech,
the Zina of the hand is the (lustful) grip,
the Zina of the feet is the walking (to the place where one intends to commit Zina)
1377. Ibn Mas`ud (May Allah be pleased with him) reported: The Prophet (sallallaahu ’alayhi wa sallam) said,
“Envy is permitted only in two cases: A man whom Allah gives wealth, and he disposes of it rightfully, and a man to whom Allah gives knowledge which he applies and teaches it.”
[Al-Bukhari and Muslim].
Commentary: According to Imam An-Nawawi‘s explanation, the word Hasad (jealousy) is used in the sense of Ghibtah i.e., envy. In Islam, jealousy is forbidden and is held unlawful. The reason being that one who is jealous wants that the person, who possesses the quality of which he is jealous, be deprived of that quality. Envy is permissible for the reason that when one seems that a person has been graced by Allah with certain gifts and qualities, he also desires to be blessed with those gifts. In the latter case, he does not grumble and grieve but eagerly prays to Allah for those gifts. `Knowledge’ here stands for the knowledge of the Qur’an and Hadith because this knowledge alone is beneficial for man, and it is through this knowledge that correct judgements can be made among the people. This Hadith has an inducement for acquiring useful knowledge along with wealth to spend in the ways ordained by Allah.
Imam Al-Nawawi’s Riyad-us-Saliheen – Book Twelve: The Book of Knowledge
Chapter 241 : Virtues of Knowledge which is Learnt and Taught for the sake of Allah
Narrated Aisha (radhi Allaahu anha) and Abdullaah bin Abbaas (radhi Allaahu anhu) :
When the last moment of the life of Allaah’s Messenger (Sallallaahu Alaihi Wasallam) came, he started putting his Khameesa (a woolen blanket) on his face and when he felt hot and short of breath he took it off his face and said, “May Allaah curse the Jews and Christians, for they built places of worship at the graves of their Prophets.”
[The Prophet (Sallallaahu Alaihi Wasallam) was warning (Muslims) of what those people had done].
[Saheeh Al-Bukhari, Hadeeth No. 427, Vol. 1]
Source :The Book of Mosques and places of worship – Chapter 3 – It is forbidden to build mosques over the graves
Al-Lulu Wal-Marjan, Compiled by : Fuwad Abdul-Baqi, Translated by : Dr. Muhammad Muhsin Khan