Abu Hurairah reported,
The Messenger of Allah ﷺ said, "The first thing for which a servant will be called to account is his prayer. If he has performed it completely, well and good. Otherwise, Allah 
will say, 'Look, does My servant have any voluntary prayers?' If voluntary prayers are found, He will say, 'Complete the obligatory prayer with them.'"
Nasai 468
Sahihأخبرنا إسحق بن إبراهيم قال حدثنا النضر بن شميل قال أنبأنا حماد بن سلمة عن الأزرق بن قيس عن يحيى بن يعمر
عن أبي هريرة
عن رسول الله ﷺ قال أول ما يحاسب به العبد صلاته فإن كان أكملها وإلا قال الله عز وجل انظروا لعبدي من تطوع فإن وجد له تطوع قال أكملوا به الفريضة
[Its chain is sahih] Ahmad transmitted it, 4/103, from the hadith of Hammad bin Salama with similar wording, except that he said, "from a man among the companions of the Prophet ﷺ" instead of "Abu Hurairah 
", and it is from him, and it is in al-Kubra, no. 325, and it has many corroborating narrations with Abu Dawud, no. 866, and elsewhere.