Will a Muslim receive the reward mentioned in the hadith if he performs ablution like the Prophet (peace and blessings be upon him) and then prays Asr, or if he has a sudden urge to urinate during two out of four rak'ahs?

If a Muslim performs ablution completely and prays two rak'ahs after it, and during them does not think about worldly matters, he will attain the reward mentioned in the hadith. However, if he thinks about something worldly, he will not attain the reward. This reward includes both obligatory and supererogatory prayers, even if performed during times when prayer is ordinarily forbidden, provided there is a reason for them. Fleeting thoughts that do not settle do not prevent the attainment of this فضْل (grace/virtue).