Seeing as the word "Tze'akah" is feminine, why does the Torah write "Kamohu" and not 'Kamohah'?
Seforno and Targum Yonasan: "Kamohu" refers to (the unwritten) night (which is masculine), and what the Pasuk means is that on such a night 1 no cry (Nih'yasah is feminine) 2 was ever heard and would never be heard again. 3
Moshav Zekenim "Kamohu" refers to the (unwritten) destruction (Shod and Shever, which is masculine).
When peace reigned (to preclude a night in time of war [Seforno]).
The Rashbam explains both words ("Kamohu" and "Nih'yasah") with reference to Laylah, and this is a case of a word which can be both masculine and feminine (even at one and the same time (See Bereishis 32:9 [Rashbam] and Rashi there).
This also answers the Kashya that the cries in Egypt following Ker'i'as Yam-Suf were surely no less than those of Makas Bechoros? Only that took place in the day (in the early morning) and not at night-time [Peirush Yonasan]).