Asim bin Damrah (may Allah have mercy on him) said: We were with Sayyiduna Ali (may Allah be pleased with him) on a journey. He led us in the Asr prayer as two rak'ahs and went into his tent, and I was watching; then he prayed two rak'ahs.
Al-Shafi'i (may Allah have mercy on him) related these three hadiths from Ali (may Allah be pleased with him), then said: These are hadiths, some of which contradict others. The Shaykh (may Allah have mercy on him) said: What is obligatory upon us, then, is to follow that in which no disagreement has occurred; then (the prohibition) is restricted to prayers that have no cause, and prayers that have a cause are excepted from the prohibition by the report of Sayyidah Umm Salamah (may Allah be pleased with her) and others. Wallahu a'lam (Allah knows best).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4406