Answered by Shaykh Faraz Rabbani
Question: When a husband leads his wife alone in prayer, where does wife stand? Is it better for them to pray in congregation or pray alone?
It is best for her to stand completely behind her husband, though it is valid, according to the relied upon opinion, as long as his heel is in front of hers. [Radd al-Muhtar]
It is not disliked for a man to pray in congregation with his wife alone. In fact, the basic reward of praying in congregation is attained in this way. It is better, for the man, to pray in congregation with his wife than alone if he misses congregational prayer in the mosque. [Radd al-Muhtar]
This is very useful for people whose work schedule makes them miss maghrib or isha in the mosque; they should make arrangements with their spouses to pray together. However, the fuqaha caution that this would be blameworthy to make a habit without excuse, as it is expected of Muslim men that they pray at the mosque.
Abu Hurayra (Allah be pleased with him) related that the Messenger of Allah (Allah bless him & give him peace) said, “If people knew what [reward] there is in the call to prayer and the first row, and then they found no way but to draw ots [to attain them], they would have drawn lots. And if they knew what [reward] there is in being early, they would have raced each other to it. And if they knew what [reward] there is in the night prayer [isha] and dawn prayer, they would come to it, even if crawling.” [Bukhari 580, and elsewhere]
And Allah knows best.