Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: The person who gives people a fatwa on every matter about which they ask him for a fatwa has madness in him.
Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 859