Sayyiduna Anas (may Allah be pleased with him) narrates: When the Companions heard the adhan for Maghrib, they would get up and start performing nawafil as if these were obligatory.
Hadith Referenceسنن الدارقطني / كتاب الصلاة / 1049
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 1047، انفرد به المصنف من هذا الطريق»