Sa'id bin al-Musayyab (may Allah have mercy on him) narrates from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that the impotent man is to be given a respite of one year. If he becomes able, (well and good); otherwise they are to be separated. The woman is entitled to the mahr, and she must observe the iddah.
The Shaykh (may Allah have mercy on him) said: This is based on his view that seclusion (khalwah) establishes the mahr and makes the iddah obligatory.
(b) Al-Sha'bi (may Allah have mercy on him) narrates from Sayyiduna Umar (may Allah be pleased with him) in mursal form that the one-year respite is to be counted from when the case is presented before the ruler.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14289