Muwatta Malik 1760

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ أَبِي طَلْحَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ سَمِعَ عُمَرَ بْنَ الْخَطَّابِ، وَسَلَّمَ، عَلَيْهِ رَجُلٌ فَرَدَّ عَلَيْهِ السَّلاَمَ ثُمَّ سَأَلَ عُمَرُ الرَّجُلَ كَيْفَ أَنْتَ فَقَالَ أَحْمَدُ إِلَيْكَ اللَّهَ ‏.‏ فَقَالَ عُمَرُ ذَلِكَ الَّذِي أَرَدْتُ مِنْكَ ‏.‏

Yahya related to me from Malik from Ishaq ibn Abdullah ibn Abi Talha that Anas ibn Malik heard Umar ibn al-Khattab return the greeting of a man who greeted him. Then Umar asked the man, "How are you?" He said, "I praise Allah to you." (Ahmadu ilayka Allah) Umar said, "That is what I wanted from you

Reference

Muwatta Malik 1760

In-book

Book 53, Hadith 5