Sheikh Muhammad b. Sâlih al-`Uthaymîn
It is not prescribed for a person upon completing prayer to raise his hands in supplication. If the person wishes to offer supplications, he should know that offering the supplication while in prayer is better than offering it after completing the prayer.
This is what our Prophet (peace be upon him) guided us to. In a hadîth narrated by Ibn Mas`ûd, when the Prophet (peace be upon him) mentioned completing the tashahhud, he said: “Then he should offer any supplication that he wishes.” [Sahîh al-Bukhârî and Sahîh Muslim]
What we see some people doing is that every time they offer a prayer, as soon as they say the taslîm they invariably raise their hands. Sometimes they do so for such a brief moment that is scarcely enough time to actually supplicate – but is more like a formality of raising the hands – and then some of them wipe their faces. They offer up this practice after each prayer to preserve what they think is a prescribed act of supplication.
However, no such act is prescribed. Making such an unwavering habit of doing so actually becomes an innovation.
And Allah knows best.
Source: Islam Today