Sometimes, in the middle of my fardh prayer, I feel like I'm going too fast and that I'm not focusing on the prayer. Is it ok to leave in the middle of the prayer and start it again right away with more khushooh or should I renew my intention in the original prayer and continue?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is not permissible to interrupt an obligatory prayer without a legitimate justification. The Fiqh Encyclopedia reads: Interrupting an obligatory worship after starting it without a legitimate justification is not permissible according to the agreement of the jurists because interrupting it without a legitimate justification is a futility that contradicts the sanctity of worship. The prohibition against invalidating worship is mentioned in the Saying of Allah (which means): {And do not invalidate your deeds.} [Quran 47:33] As for interrupting it for a legitimate justification, then it is lawful, so the prayer is interrupted to kill a snake and the like, for the order to kill it and for fear of losing money of value, for him or someone else, and for the relief of the distressed, and to alert the heedless (who is unaware of the possible danger), or sleeper to whom a snake is heading and cannot be alerted by Tasbeeh (praising Allah). Similarly, fasting is interrupted to save a drowning person, fearing for a soul or a baby.” [End of quote]

The mere feeling of haste or suspicion of something invalidating the prayer is not an excuse; rather, it is likely that it is a whisper of the devil (Waswas). Unless one knows without a doubt that he is too fast, in a way that undermines the pillar of tranquility in prayer, then the prayer is invalid in this case, whether he ended it or not. The jurists explained the rule of tranquility in prayer. Al-Mardawi  said in Al-Insaf: “Its limit is obtaining the tranquility even if it is little, according to the correct view of the Madhhab (i.e, the Hanbali School of jurisprudence).” Accordingly, the pillar of tranquility is achieved by the body parts being steady in each part of the prayer for a certain period, even if it is little.

Likewise, if he misses Khushoo’ [proper focus, submissiveness, humility and reverence in Prayer] in any part of the prayer, he should not interrupt it, but he should try to attain it in the rest of it. The jurists stipulated that the prayer should not be interrupted even to relieve oneself (call of nature) after he started it. Tuhfat al-Muhtaj reads: “He (the praying person) is neither permitted to interrupt an obligatory prayer if an obstacle occurs to him, nor delay it [obligatory prayer] it if its time is short... However, some of them (jurists) permitted to interrupt the obligatory prayer if he missed the Khushoo’ in it, but this is not a strong or substantial view.” [End of quote]

For more benefit about Khushoo' in Prayer, please refer to Fatawa 384499, 415666, 74911 and 448732.

For more benefit on observing Tuma'neenah in prayer, please refer to Fatawa 180233, 200531, 350416, 338716, 391381 and 326782.

Allah knows best.