Question 137: The time of Duhr (Noon) Prayer was due when I was at a place where there was no water, so I offered Duhr Prayer after performing Tayammum (dry ablution with clean earth). After Salaah, I was sure that my Tayammum had not been invalidated until the time of ‘Asr (Afternoon) Prayer was due, so I offered Salaah without performing Tayammum again. Is the second Salaah valid or not? Should I perform Tayammum after the time of each prayer is due?
Answer: All praise be to Allaah Alone, and peace and blessings be upon His Messenger, and his family and Companions. The sound view of scholars is that Tayammum is not invalidated by the end of the prayer time for which a person performed Tayammum; rather it is invalidated when water is present or by the occurrence of any of the annulments of Wudoo’ (ablution)… read more here.