This Abū Abī is a Companion who prayed facing both qiblahs; his personal name was ʿAbd Allāh. All the transmitters in his chain are reliable and are found in Ṣaḥīḥ Muslim, except for Abū al-Muthannā—whose name is Ḍamḍam al-Amlūkī. Ibn Ḥibbān declared him trustworthy, as recorded in al-Khulāṣah, and al-ʿAjlī likewise graded him reliable in al-Taqrīb. Nothing further is reported about him, so the isnād is sound or at least capable of being upgraded; Allah knows best.

(2) The narration of Ibn Masʿūd, which comes by two routes:

First route: through ʿAbd al-Raḥmān ibn Sāyiṭ, from ʿAmr ibn Maymūn, from Ibn Masʿūd—marfūʿ—with the wording:

“How will you fare when rulers appear who perform the prayer outside its appointed time?”
I asked, “O Messenger of Allah, what do you command me to do if that happens?”
He said, “Pray at its prescribed time, and count the prayer you perform with them as a supererogatory one.”

Abū Dāwūd recorded it through al-Walīd, who said: al-Awzāʿī narrated to us; Ḥassān ibn ʿAṭiyyah narrated to me from ʿAbd al-Raḥmān ibn Sābiṭ—who related it.

This chain is ṣaḥīḥ, provided it is free from the tadlīs of al-Walīd (Ibn Muslim), for he practiced tadlīs al-taswiyah. All of the other transmitters are those used by Muslim.

Second route: from Zirr, from Ibn Masʿūd—may Allah be pleased with him—with the wording:

“Very likely you will encounter people who perform the prayer outside its proper time. When that happens, pray in your houses at the time you recognize, then join them in their prayer and regard it as a supererogatory act.”

Aḥmad (1/379) recorded it through Abū Bakr, who said: ʿĀṣim narrated to us, from Zirr. This isnād is ḥasan.