What are extravagance and squandering in the Qur'an and Sunnah?

There are numerous Quranic verses that condemn the extravagant, and many Prophetic traditions (hadiths) that call for moderation and temperance, some of which are authentic and some weak. Among the authentic hadiths are: Jabir ibn Abdullah's hadith in Muslim: "A bed for a man, a bed for his wife, a third for the guest, and the fourth for the devil." And Al-Tirmidhi's hadith from Abdullah ibn Sarjis: "Good conduct, deliberation, and moderation are one of twenty-four parts of prophethood." And Al-Nasa'i's hadith from Amr ibn Shu'ayb: "Eat, give charity, and wear (clothes) without extravagance or boastfulness." Among the hadiths that are weak is: Abu Darda's hadith in Musnad Ahmad: "It is from a man's understanding to be moderate in his livelihood," though it is authentically reported that the Prophet, peace and blessings be upon him, said: "He who is moderate will not become poor."