Rule 1: 1. The three oath particles
(a) وَ is the commonest particle in speech and writing: وَاللّٰهِ, وَحَقِّ الْقُرْآنِ by the truth of the Quran. (b) بِـ must be used when the verb of swearing is expressed, أُقْسِمُ بِاللّٰهِ or حَلَفْتُ بِاللّٰهِ I swear / swore by God, and when the thing sworn by is a pronoun: بِكَ by You. (c) تَ is used only with the word اللّٰه, تَاللّٰهِ, and is rare outside the Quran and solemn style; it often expresses astonishment. In all three cases the noun is in the genitive.
وَاللّٰهِ مَا رَأَيْتُهُ.
wa-llāhi mā raʾaytuhu
By God, I did not see him.
وَ + genitive; negative answer with مَا.
أُقْسِمُ بِاللّٰهِ الْعَظِيمِ أَنْ أَقُولَ الْحَقَّ.
uqsimu bi-llāhi l-ʿaẓīmi an aqūla l-ḥaqqa
I swear by Almighty God to tell the truth.
Verb of swearing expressed, so بِـ; the adjective follows in the genitive.
حَلَفَ بِاللّٰهِ أَنَّهُ لَمْ يَأْخُذِ الْمَالَ.
ḥalafa bi-llāhi annahu lam yaʾkhudhi l-māla
He swore by God that he had not taken the money.
حَلَفَ بِـ + أَنَّ in reported oaths.
تَاللّٰهِ لَقَدْ صَدَقْتَ!
ta-llāhi la-qad ṣadaqta
By God, you have spoken the truth!
تَ: only before اللّٰه; a tone of wonder.
وَحَقِّ الْقُرْآنِ لَا أَكْذِبُ عَلَيْكَ.
wa-ḥaqqi l-qurʾāni lā akdhibu ʿalayka
By the truth of the Quran, I will not lie to you.
حَقِّ is genitive after وَ, and الْقُرْآنِ genitive in the iḍāfa.