One who after upanayanam, having undergone samashrayanam, if they do not perform trikaala sandhyavandanam, will one get the benefit of having done prapatti through an Acarya? Is trikaala sandhyavandanam a must for prapatti? It is said that one who does not perform sandhyavandanam is not qualified to perform rituals ordained by the Vedas. Is the rule applicable for prappatti?

Even when one does not perform sandhyavandanam, one will get the benefits of performing prapatti. These are not related. It is a general rule that one must perform sandhyavandanam whether one has or has not undergone samashrayanam and bharanyasam.

Not performing sandhyavandanam will beget sin and will lose the qualification to perform other karmAs.

Notes:

For example, what if one who has performed sharanagati decides to lie? If they ask “Does lying beget sin?” It is a fundamental rule that one must not lie; no doubt lying will certainly beget sin.

Similarly, performance of sandhyavandanam is mandatory; this will not impact sharanagati in any way. Both are independent of each other.