Sunan an-Nasa'i — The Book of Salah — Hadith No: 465
Translation
It was narrated that Huraith bin Qabisah said:"I arrived in Al-Madinah and said: 'O Allah, make it easy for me to find a righteous companion.' Then I sat with Abu Hurairah, may Allah be pleased with him, and said: 'I prayed to Allah to help me find a righteous companion.' So tell me a Hadith that you heard from the Messenger of Allah (ﷺ), so that Allah might benefit me from it. He said: 'I heard the Messenger of Allah (ﷺ) say: "The first thing for which a person will be brought to account will be his Salah. If it is sound then he will have succeeded, be salvaged, but if it is not then he will have lost and be doomed." - (One of the narrators) Hammam said: "I do not know whether this was the words of Qatadah or part of the report." - "If anything is lacking from his obligatory prayers, He will say: 'Look and see whether My slave has any voluntary prayers to make up for what is deficient from his obligatory prayers.' Then all of his deeds will be dealt with in like manner