Has it been reported from the Prophet (PBUH) that he prayed four rak'ahs before 'Ishā' and four rak'ahs after the Sunnah of 'Ishā'?

There is no regular sunnah prayer before Isha. However, it is prescribed for the worshipper to pray two rak'ahs before Isha, based on the Prophet's (peace be upon him) saying: "Between every two adhans there is a prayer, between every two adhans there is a prayer," then he said for the third time, "for whoever wishes."

As for the post-Isha sunnah prayers: The regular sunnah is two rak'ahs after Isha, as narrated by Ibn Umar (may Allah be pleased with them both), who said: "I memorized from the Prophet (peace be upon him) ten rak'ahs: ... and two rak'ahs after Isha in his house."

It is permissible to increase upon the two rak'ahs before or after Isha, and that is considered part of the night vigil (Qiyam al-Layl).