Sunan Abi Dawud 800
سنن أبي داود#800Sahihحَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنْ يَحْيَى، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي قَتَادَةَ، عَنْ أَبِيهِ، قَالَ فَظَنَنَّا أَنَّهُ يُرِيدُ بِذَلِكَ أَنْ يُدْرِكَ النَّاسُ الرَّكْعَةَ الأُولَى .
Abu Qatadah said:We thought that by this (prolonging the first rak’ah). He (the prophet) meant that the people might join the first rak’ah
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Bukhari (776) Sahih Muslim (451)
In-book reference: 2:410