The imperfect active begins as يَبِيعُ, and the passive as يُبَاعُ. The passive has the initial prefix with ḍammah and a long ā internally.
PositionActive imperfectPassive imperfect
هُوَيَبِيعُيُبَاعُ
هُمَا (م)يَبِيعَانِيُبَاعَانِ
هُمْيَبِيعُونَيُبَاعُونَ
هِيَتَبِيعُتُبَاعُ
هُمَا (ف)تَبِيعَانِتُبَاعَانِ
هُنَّيَبِعْنَيُبَعْنَ
أَنْتَتَبِيعُتُبَاعُ
أَنْتُمَا (م)تَبِيعَانِتُبَاعَانِ
أَنْتُمْتَبِيعُونَتُبَاعُونَ
أَنْتِتَبِيعِينَتُبَاعِينَ
أَنْتُمَا (ف)تَبِيعَانِتُبَاعَانِ
أَنْتُنَّتَبِعْنَتُبَعْنَ
أَنَاأَبِيعُأُبَاعُ
نَحْنُنَبِيعُنُبَاعُ
The feminine plural gives يَبِعْنَ and يُبَعْنَ. The long vowel is shortened, and the voice distinction is reflected in the remaining short vowels.