What is the manner of tayammum and what are its invalidators?

The questioner : What is the manner of tayammum, what invalidates it, and what should one do if he finds water sufficient for part of his wudu?

The Shaykh : The manner of tayammum is to strike the earth with both hands once, then wipe his entire face with the palms of his hands, then wipe his right hand with his left and vice versa. This is the prescribed manner. The scholars said: It is recommended that he interlace his fingers.
As for what invalidates tayammum, if the tayammum was for major ritual impurity, it is invalidated by anything that obligates the full ritual bath. If it was for the ablution, it is invalidated by what invalidates the ablution, as long as the permissibility of tayammum remains. However, if tayammum is no longer permissible, such as if one performs tayammum due to the absence of water and then finds it, his tayammum is invalidated by the presence of the water. Likewise, if he performs tayammum due to an illness and then recovers from it, his tayammum is invalidated by his recovery from that illness. Tayammum is not invalidated by the passing of the time according to the stronger opinion. This is because the Prophet (peace and blessings be upon him) said: and "al-tahur" (with a fathah) is that by which one purifies oneself, just as "al-wudu" (with a fathah) is that by which one performs ablution, and "al-suhur" (with a fathah) is that by which one eats the pre-dawn meal. And Allah (Mighty and Majestic) said, after mentioning purification with water and tayammum: This indicates that tayammum is a purifier. And if it is a purifier, its purity is not invalidated except by what invalidates the purity of water, because tayammum is a substitute for it, and the substitute has the ruling of the thing it substitutes. So if a person performs tayammum for major ritual impurity, for example, his state of impurity is lifted, and he does not repeat the tayammum for that major ritual impurity unless he incurs another major ritual impurity or another cause for the full ritual bath. And if he performs tayammum for one of the things that invalidate the ablution, he remains in a state of purity until one of the invalidators occurs. So if a man performs tayammum for the Fajr prayer and remains in his state of purity until the Zuhr prayer or the 'Asr prayer, and no invalidator of the ablution has occurred, such as urination, sleep, defecation, eating camel meat, or anything else that invalidates the ablution, then in this case he prays with the tayammum he performed for the Fajr prayer.