Allaah (The Most High) said:

يَسۡـَٔلُونَكَ مَاذَآ أُحِلَّ لَهُمۡ‌ۖ قُلۡ أُحِلَّ لَكُمُ ٱلطَّيِّبَـٰتُ‌ۙ وَمَا عَلَّمۡتُم مِّنَ ٱلۡجَوَارِحِ مُكَلِّبِينَ تُعَلِّمُونَہُنَّ مِمَّا عَلَّمَكُمُ ٱللَّهُ‌ۖ فَكُلُواْ مِمَّآ أَمۡسَكۡنَ عَلَيۡكُمۡ وَٱذۡكُرُواْ ٱسۡمَ ٱللَّهِ عَلَيۡهِ‌ۖ وَٱتَّقُواْ ٱللَّهَ‌ۚ إِنَّ ٱللَّهَ سَرِيعُ ٱلۡحِسَابِ

They ask you (O Muhammad) what is lawful for them (as food). Say: “Lawful unto you are At-Tayyibat[all kind of Halal (lawful-good) foods which Allah has made lawful (meat of slaughtered eatable animals, milk products, fats, vegetables and fruits, etc.)]. And those beasts and birds of prey which you have trained as hounds, training and teaching them (to catch) in the manner as directed to you by Allah; so eat of what they catch for you, but pronounce the Name of Allah over it, and fear Allah. Verily, Allah is Swift in reckoning.” [5:4]

Imaam Ibnul Qayyim (rahimahullaah) said: Indeed, Allaah (Glorified Be He) made the prey of the untrained hound a dead meat and unlawful to eat! And He made lawful the prey of the trained hound. This is from the nobility of knowledge, (for) indeed He did not make lawful except the prey of the trained hound. As for the untrained hound, its prey is not permissible to be eaten. Therefore, this shows the nobility and virtue of knowledge. Had it not being for the marked distinction of knowledge and teaching, and its nobility, the trained and untrained hound would have been the same.

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[Mihtaah Daarus Sa’aadah. 1/55]