Al-Yazid ibn Abd al-Qadir Ustadz Jawas
Useful science can be known by looking at the owner's science. Among the signs are:
A. Rewarding those who do not care about the state of his science and position themselves and their hearts to hate praise of men, did not consider himself pure, and not overbearing to others with the science they have.
Imam al-Hasan al-Basri (d.. 110 H) rahimahullaah said, "People are just people who ascetic faqih of the world, are looking forward to the afterlife, know his religion, and diligent in worship." In another narration he said, "He not jealous of people who are on it, not arrogant against people who are under it, and do not take benefits from the science that Allah taught him. "
2. The beneficial owner of the science, if his science increases, they are increased tawadhu attitude ', fear, humiliation, and ketundukannya in the presence of God Almighty.
3. Science is Useful to invite the owner to escape the world. The biggest one is the status, fame, and praise. Away from it and meant it in her away, then it is a sign of Useful science.
4. The owner of this science is not to claim to have science and are not proud of him for one. He does not attribute ignorance to anyone, except someone who clearly violated the Ahlus Sunnah and the Sunnah. He was mad at him because Allah Ta'ala alone, not for personal, nor is it intended to elevate the position himself above anyone. 
Shaykh al-Islam Ibn Taymiyah (d.. 728 H) rahimahullaah share this Useful science, which is the pillar and the principle of wisdom into three parts. Rahimahullaah He said, "Science is commendable, as demonstrated by the Book and the Sunnah is the science which is inherited from the Prophets, as the Prophet sallallaahu spoken 'alaihi wa sallam.
"Verily, the scholars are the inheritors of the Prophets, and they do not pass dinar nor dirham. They just pass on science. Who took it, then he has taken a lot of parts. "
It Has Three Kinds of Science:
A. Science of God, Names, and his qualities as well as matters related to it. An example is as Allah revealed Surat al-Ikhlaash, verse Chair, and so forth.
2. Science about the news from God about the things that have happened and will happen in the future and that is happening. An example is Allah revealed the verses of the story, promises, threats, the nature of Heaven, the nature of Hell, and so forth.
3. Science of God's commands relating to the hearts and deeds of the body, such as faith in God, and the science of the heart condition, and the words and deeds of the limbs. And it is entered in it the science of the fundamentals of faith and of Islamic rules and principles include the science which deals with words and deeds are obvious, such as the sciences of fiqh that discuss legal deeds. And it is part of the science of religion. 
Shaykh al-Islam Ibn Taymiyah (d.. 728 H) rahimahullaah also said, "It has been said Yahya ibn 'Ammar (d.. 422 H),' Science that there are five:
A. Which is a life science for religion, the science of monotheism
2. Which is a fine science of religion, the science of studying the meanings of the Qur-an and hadith
3. Science is a religion of medicine, the science fatwa. If a catastrophe (catastrophe) came to a servant, he needs someone who can cure him of the accident, as stated by Ibn Mas'ud radhiyallaahu 'anhu
4. Science is a religion of disease, the science and innovation kalam, and
5. Science which is the destruction of religion, witchcraft and the like. '"