The particle laa (لا) when preceding a noun in Arabic generally negates the entire category - it can however be used to prohibit an act implied by the noun.
So the phrase:
لاَ إِلَهَ إلاَّ اللهُ
"Laa ilaaha illallah"
There is no God but Allah
negates all categories of "gods" - except Allah.
The following verse has been understood conversely:
الْحَجُّ أَشْهُرٌ مَّعْلُومَاتٌ فَمَن فَرَضَ فِيهِنَّ الْحَجَّ فَلَا رَفَثَ وَلَا فُسُوقَ وَلَا جِدَالَ فِي الْحَجِّ
The Hajj (are) months well known, then whoever undertakes therein the Hajj then no sexual relations and no wickedness and no quarrelling during the Hajj. (Qur'an 2:197)
Sexual relations, wickedness and quarrelling are forbidden during the hajj period. Here the particle laa does not mean a negation in terms of acts of sexual intercourse, wickedness or quarrelling whilst in the state of sanctity (ihram) but to clarify the prohibition of such actions.
Whilst the hadith about usury has been understood both ways:
لاَ رِبَا بَيْنَ مُسْلِمٍ وَحَرْبِيٍ فِي دَارِ الحَرْبِ
"Laa riba bayna Muslim wa al-harbi fii dar il-harb"
No usury between the Muslim and the one he is at war with (Al-Shafi'i, Al-Umm; Al-Sarakhsī, Usūl al-Sarakhsī; Al-'Aynī, Al-Bināyah Sharḥ al-Hidāyah)
Ibn Qudamah's interpretation of the hadith would suggest no usury can take place between a Muslim and a harbi in the land of war whilst the Hanafis and some Hanbalis argued a Muslim granted safe passage into Dar al-Harb (or musta'man) was allowed to deal in interest with citizens of Dar al-Harb (harbıs).
The particle laa can be used for both and examples appear in the Qur'an and ahadith for both usages.
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