Does anything become incumbent upon me if I deliberately say something disrespectful towards Allah Almighty to myself during the last Tashahhud in prayer, knowing that I am unsure whether that was a slip of the tongue, an intentional utterance, or an act of hastiness?

One who utters words constituting apostasy by mistake is not judged an apostate, because the apostasy by which a Muslim becomes an unbeliever is the embracing of disbelief with an open heart. The proof for this is Allah’s saying: {Whoever disbelieves in Allah after his belief, except for one who is forced [to renounce his religion] while his heart is secure in faith. But those who embrace disbelief with open hearts—upon them is wrath from Allah, and for them is a great punishment} [An-Nahl: 106]. And whatever was merely a slip of the tongue or a mistake does not harm, for the Prophet (peace and blessings be upon him) said: “My Ummah has been forgiven for mistakes, forgetfulness, and what they are forced to do.” Moreover, the lack of certainty that the word was uttered intentionally or hastily is a sign of waswasah (whispers from Satan), and as long as the possibility exists, there is nothing upon the speaker. The scholars have mentioned that whoever utters words that could mean apostasy or something else is not to be declared an apostate for that. And if there are ninety-nine reasons pointing to the apostasy of a Muslim and one reason to keep him in his Islam, then the mufti and the judge should act upon that one reason.