Is the prayer of one who forgot the Tashahhud in the second rak'ah of the Asr prayer, then completed the Tashahhud before the Taslim, then remembered and completed his prayer and performed the prostration of forgetfulness (sujud al-sahw) after the fourth rak'ah, valid? And was his prostration in its correct place?

If a worshipper adds to the first tashahhud by reciting the salat on the Prophet (peace be upon him) and the invocations usually recited in the final tashahhud, some scholars hold that he is not required to perform the prostration of forgetfulness (sujud al-sahw). However, others consider sujud al-sahw to be prescribed for this type of error. If the worshipper performs the prostration of forgetfulness for this addition, his prostration is appropriate and prescribed.