Tabdhir - The prohibition of spending wastefully
The Qur'an expresses the sense of spending wastefully through two words: (1) Tabdhir, translated as 'squandering recklessly'. (2) Israf, extravagance.
The prohibition of tabdhir is already clear in verse 26 of Surah Bani Isra'il (Al Isra). The prohibition of Israf has its proof in the verse of Surah al-A'raf (and do not be extravagant - 7:33).
Some commentators say that both words are synonymous. Any spending in sin or disobedience or a wrong occasion or place is called tabdhir and israf.
There are others who refine it by saying that tabdhir is pending in sin or in some totally unsuitable occasion or place, while israf is spending beyond the level of need on an occasion where it is permissible to spend.
Therefore, tabdhir is emphatically worse than israf. Al-Mubadhirin (the slanderers) were called brothers to shaitan and his corhorts.
Of the earlier Tafsir authorities, Mujahid has said,
"If someone spends everything he his for the sake of what is haqq, (incumbent), it is not tabdhir (squandering recklessly) - and should he spend even one mudd (1/2 kilo) for what is false (non-incumbent), then it is tabdhir"
Sayyidina Abdullah ibn Mas'ud (may Allah may pleased with him) said,
"Spending out of place in what one has not been obligated with is tabdhir." (Mazahir)
Imam Malik said,
"Tabdhir is that one aquires wealth and property, lawfully and cleanly, as he has been obligated to do so, but spends it off in ways counter to it - and this is also given the name of israf (extravagance), which is haram (unlawful)."
Imam al-Qurtubi said,
"As for things unlawful and impermissible, spending even one dirham for these is tabdhir. And spending limitlessly to fulfill permissable and allowed desires - which exposes one to the danger of becoming a needy begger in the future - is also under tabdhir.
Yes, if someone keeps his real capital holdings in tact and goes on to spend its profit liberally to fulfill his permissable desires, then, that is not included under tabdhir." (Al-Qurtubi, v. 10, p. 248)