How authentic is the Hadith: "Do not belittle any good deed..."?

Al-Nasa'i narrated a hadith (definition) from Al-Hujaymi describing his meeting with the Prophet, peace and blessings be upon him, and that the Prophet taught him that saying "peace be upon you" is for the dead, and advised him not to belittle any good deed. Imam Ahmad also reported a hadith with a similar wording and an authentic chain of narration, in which Al-Hujaymi mentions his meeting with the Prophet, peace and blessings be upon him, who taught him the correct greeting of peace, the proper place for the izar (lower garment), and advised him not to belittle any good deed, such as giving a piece of rope or a shoelace, emptying a bucket into the vessel of one seeking water, removing harm from the path, meeting people with a cheerful face, comforting the lonely, and he forbade him from cursing anyone who cursed him with something he knew about them, and to do what pleases his hearing and avoid what displeases him. Abu Ubayd al-Qasim bin Salam explained the importance of performing good deeds, even if they are small, and that whoever belittles a small good deed will be deprived, and a small deed can have a great impact on someone in need.