Hadith: You have followed the Sunnah and your (first) prayer was enough for you

عن أبي سعيد الخدري رضي الله عنه قال: خرج رَجُلَان في سفر، فَحَضَرَتِ الصلاة وليس معهما ماء؛ فَتَيَمَّمَا صَعيدا طيِّبا فَصَلَّيَا، ثمَّ وجَدَا الماء في الوقت، فأعاد أَحَدُهُمَا الصلاة وَالوُضُوءَ ولم يُعِدِ الآخر، ثم أتَيَا رسول الله صلى الله عليه وسلم فذكَرَا ذلك له فقال لِلَّذِي لَمْ يُعِدْ: «أَصَبْتَ السنة، وَأَجْزَأَتْكَ صَلَاتُكَ». وقال للذي توضأ وأعاد: «لك الأجر مرَّتَين».
[صحيح] - [رواه أبو داود والنسائي والدارمي]

Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported: Two men set out on a journey, and prayer became due while they had no water. They performed dry ablution, using clean earth, and prayed. Later on, they found water while still within the time of the prayer. One of them repeated his prayer with ablution, and the other did not. Then, they came to the Messenger of Allah (may Allah’s peace and blessings be upon him) and informed him about that. He said to the one who did not repeat his prayer: "You have followed the Sunnah and your (first) prayer was enough for you." He then said to the one who performed ablution and repeated his prayer: "For you there is a double reward."
[Authentic hadith] - [An-Nasaa’i - Narrated by Abu Daoud - Ad-Daarimi]

Explanation

The noble Companion Abu Sa‘īd al-Khudri (may Allah be pleased with him) relates: “Two men set out on a journey, and prayer became due”, meaning: its time came. “While they had no water. They performed dry ablution, using clean earth”, meaning: they turned to the earth and used it in the way specified for dry ablution. “Later on, they found water while still within the time of the prayer. One of them repeated his prayer with ablution”, meaning: either because he thought his first prayer was rendered invalid or he simply wanted to err on the side of caution. “And the other did not”, meaning: based on the thought that his first prayer remained valid. They then went to the Messenger of Allah (may Allah’s peace and blessings be upon him) and mentioned what happened to him. To the man who did not repeat the prayer, the Prophet (may Allah's peace and blessings be upon him) said: “You have followed the Sunnah”, meaning: your act accorded with the established teachings of the Sunnah. “He then said to the one who performed ablution and repeated his prayer: ‘For you there is a double reward”, meaning: you will have a double reward for your prayers, for both are valid and each entails a reward, and indeed Allah does not cause the good deeds of His slaves to go to waste. This indicates that it is better to do what is safer and more cautious. In another Hadīth, the Prophet (may Allah's peace and blessings be upon him) said: “Leave what is doubtful for what is not doubtful.”