Is the supplication of the one leading the Tahajjud prayer, "O Allah, have mercy on us... I adjure You to have mercy on us... O Lord, say now: 'Go, My servants, for I have forgiven you now... now... now, O Lord, say now, O Lord, I have pardoned you,'" considered an overstepping of bounds with Allah and not in keeping with the etiquette of supplication?

It is permissible to swear by Allah regarding matters of goodness for one who knows himself to be righteous and steadfast. As for the other forms of supplication mentioned, they are not befitting of Allah and were not customary among the righteous predecessors. The supplicant should show humility to Allah and praise Him with that which befits His greatness and majesty.