Is it permissible for the Asr prayer to be performed as a "collection by advancement" (jam' taqdim) if the travel is delayed until after the Asr athan?

If you combined the prayers in your home before traveling, you either combined them by shortening (qasran) or by completing (itmaman). If you combined them by shortening, your prayer is invalid and must be re-performed, because shortening is not permissible until after one has commenced travel and passed beyond the city limits. However, if you combined them by completing without shortening, scholars have differed regarding its permissibility. The majority prohibit it, while some permit it, citing the Prophet's (peace be upon him) combining prayers in Madinah without fear or travel. The more cautious approach is to re-perform the second prayer. It is important to note that travel concessions are not permissible until one has commenced travel and passed beyond the city limits.