Abu Hurairah said to me, "When you reach the people of your land, inform them that I heard the Messenger of Allah ﷺ say, 'The first matter for which the Muslim servant will be called to account on the Day of Resurrection is the obligatory prayer. If he has performed it completely, well and good. Otherwise, it will be said, "Look, does he have any voluntary prayers?" If he has voluntary prayers, the obligatory prayer will be completed from his voluntary ones. Then the rest of his obligatory deeds will be treated in the same way.'"
حدثنا أبو بكر بن أبي شيبة ومحمد بن بشار قالا حدثنا يزيد بن هارون عن سفيان بن حسين عن علي بن زيد
قال لي أبو هريرة إذا أتيت أهل مصرك فأخبرهم أني سمعت رسول الله ﷺ يقول إن أول ما يحاسب به العبد المسلم يوم القيامة الصلاة المكتوبة فإن أتمها وإلا قيل انظروا هل له من تطوع فإن كان له تطوع أكملت الفريضة من تطوعه ثم يفعل بسائر الأعمال المفروضة مثل ذلك
Its isnad is daif. Abu Dawud narrated it, Book of Prayer, chapter on the Prophet's ﷺ statement, "Every prayer that its performer does not complete in full will be completed from his voluntary prayer," hadith no. 864, from the narration of Hasan from Anas bin Hakeem with this wording. Hakim graded it sahih, as did Dhahabi. The following hadith serves as a corroborating witness for part of it.