Ibn Tawus narrates from his father that Abu Ayyub al-Ansari (may Allah be pleased with him), with whom the Prophet (peace and blessings be upon him) had stayed, used to pray two rak'ahs after sunset, before the prayer, with Abu Bakr al-Siddiq (may Allah be pleased with him); he did not pray them with Umar (may Allah be pleased with him), and he used to pray them with Uthman (may Allah be pleased with him). This was mentioned to him, so he said: I prayed this prayer with the Prophet (peace and blessings be upon him), then I prayed it with Abu Bakr al-Siddiq (may Allah be pleased with him); then I was afraid of Umar (may Allah be pleased with him), so I did not pray it with him; and I have prayed these two rak'ahs with Uthman (may Allah be pleased with him), because he was gentle. Umar (may Allah be pleased with him) neither prayed them himself nor considered praying them correct, so Abu Ayyub al-Ansari (may Allah be pleased with him) also did not pray them with him.
(b) It is reported from Suwayd bin Ghafalah (may Allah have mercy on him) that he said: We had abandoned them during the caliphate of Umar (may Allah be pleased with him), then we resumed them during the caliphate of Uthman (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4504