Amir bin Mas'ud (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Fasting in winter is a cool (easily won) booty."
This is mursal (its chain does not reach a Companion who heard it).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8454
Sayyiduna Anas (may Allah be pleased with him) narrates that Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: "Shall I not tell you of the cool booty?" He says: We said: "Of course; what is it?" He said: "Fasting in winter."
This is mawquf (the words of the Companion, not of the Prophet).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8455
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Winter is the springtime of the believer: its days are short, so he fasts; its nights are long, so he stands (in prayer)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8456